Prof Patrice Woisel

Dr Didier Gigmes

Dr Simon Harrisson

Prof Rinaldo

Prof Lauth-De Nancy

Dr Jean-Daniel Viguerie

Marty

Caroline Toppan

Pierre Lavedan

Yannick

D Ciuculescu-Pradines

Clé Ment

B Lonetti

C Mingotaud

Anne-Franç Oise

C Coudret

Mingxi, Baptiste, Alexis, Marjorie, Liming and Faniry for their encouragement, kindness B Farias-Mancilla

always available, patient and passionate to discuss the thesis project process and to help me find the solutions to problems

Introduction

Stimuli-responsive or so-called "smart" (co)polymers have aroused great attraction in recent years due to the alteration of their physicochemical properties (solubility, chain conformation, aggregation properties…) to adapt to the changes of the external environment.

These rapid and reversible responsiveness endow such (co)polymers with multiple potential applications (such as drug delivery and controlled release, sensors, smart textiles, functionalized membranes…).

Responsive mechanism is attributed to the modification of inter-or intramolecular interactions induced by a response to the stimulus. Moreover, the level of response is strongly dependent on external conditions (such as the nature of stimulus and its intensity, selected solvents, presence of additives…) and (co)polymer structural parameters (such as architecture (block, statistical...), composition, (co)polymer concentration, molecular weight and dispersity).

The main objectives of this thesis are to study the relationship between composition, microstructure of different families of (co)polymers and their ability to respond to an external stimulus (temperature, pH or CO2 addition). The modification of physicochemical properties of these (co)polymers in solution (solubility, self-organization ability) is more specifically studied. Moreover, this work will provide more insights to design multi stimuli-responsive (co)polymers and to understand the complex responsive mechanism.

A bibliographic overview of thermo-, pH-and CO2-sensitive (co)polymers is presented in Chapter I. The first four sections summarize the concepts, categories and characterization techniques of thermo-, pH-and CO2-responsive (co)polymers. Some examples are given to illustrate how (co)polymer structure and composition as well as other parameters (molecular weight, polymer concentration, stimuli intensity...) influence the pahse transition and selfassembly behavior of these (co)polymers in auqeous solution upon application of different stimuli. A short overview of the synthetic strategies and typical applications of such multistimuli responsive (co)polymers is given in the end of this chapter.

Chapter II investigates the effect of copolymer composition on the formation, stabilization and catalytical properties of gold nanoparticles (AuNPs) stabilized by thermoresponsive statistical copolymer, poly((N-vinylcaprolactam)-stat-(N-vinylpyrrolinone)) (P(VCL-stat-VP)), thermoresponsive VCL moieties endow the obtained nanohybrids with an organic shell with tunable properties. Two synthetic methods are proposed to obtain such thermoresponsive nanohybrids: (1) in situ formation and (2) coating of preformed AuNPs. The effects of copolymer composition, concentration, system pH and ionic strength on the colloidal properties (size and stability) of Au@P(VCL-stat-VP) are discussed. To study the catalytic efficiency of such nanohybrids, reduction of p-nitrophenol to p-aminophenol by sodium borohydride is used as a model reaction to investigate how copolymer composition and temperature tune the reaction kinetics.

Chapter III focuses on the study of poly((n-butyl acrylate)-co-(N-isopropylacrylamide)) (P(BA-co-NIPAM)) copolymers with different microstructures (diblock, triblock and statistical) comprising thermosensitive NIPAM and hydrobic BA units. These copolymers with different structures and compositions are synthesized by reversible addition-fragmentation chain transfer polymerization/macromolecular design by interchange of xanthates (RAFT/MADIX). The effect of copolymer microstructures on their thermoresponsive properties and self-organization behavior in water is studied in dilute and in concentrated conditions.

Chapter IV aims at studying block copolymers comprising both thermo-and pHresponsive blocks. PNIPAM is chosen as a thermoresponsive block and poly(N,N-diethylamino ethyl acrylamide) (PDEAEAM) as a dual pH-and thermo-responsive block. All studied homopolymers and block copolymers with controlled molecular weight or composition are synthesized by RAFT polymerization. Thermoresponsiveness of PNIPAM and PDEAEAM homopolymers are first investigated along with pH change. Then the behavior of corresponding block copolymer in aqueous solution is studied as a function of pH and temperature, the effect of copolymer composition on thermosensitive properties and colloidal properties is also investigated under these two stimuli of temperature and pH.

Chapter V explores CO2-responsiveness of PNIPAM-b-PDEAEAM in water. The effect of CO2 (addition and removal) on the physiochemical properties of PDEAEAM homopolymer is first studied. Then the phase transition (Tc), self-organized nanostructures below and above Tc and reversibility are characterized upon exposure to CO2/N2 bubbling.

Chapter I

Literature Review

I.1 Introduction

Response to external stimuli is central to understanding how biological systems work, especially at the cellular level, with subsequent changes in properties and function from the molecular to the macroscopic level. Stimuli response is crucial for maintaining a normal function: the nervous system regulates the body's responses to internal and external stimuli by carrying information to and from all parts of the body through a vast network of nerve cells; membrane cell permeability and enzyme activity are modulated by concentration of molecular species in solution and so on.

The observation of various systems where such processes occur has indicated a certain number of directions for preparation of next generation systems capable of responding to stimuli in a controllable and predictable fashion. Many (co)polymers have been designed to respond to external stimuli such as a change in solvent, temperature, pH, light, magnetic or electric field, ionic factors, (bio)molecules and mechanical stress. These responses are manifested as dramatic changes in materials properties, dimensions, structures and interactions and may lead to their rearrangement or changes in their aggregation state.

In this chapter, we first presented the main families of stimuli responsive (co)polymers (thermo-, pH-and CO2-responsive), their corresponding responsive properties (phase transition temperature and self-organization behavior) upon stimuli applied/removal, impacts for affecting responsiveness, the main polymerization strategies used to obtain these (co)polymers and their applications in field of advanced science materials are described.

I.2 Thermoresponsive (co)polymers

Thermoresponsive (co)polymers in aqueous solution generally undergo a change of solubility in response to a modification of temperature. A fine hydrophobichydrophilic balance in their structure is responsible for this phenomenon. Small temperature changes around a critical value induce the collapse or expansion of 10 10 Chapter I. Literature Review (co)polymer chains as a response to the new adjustments of hydrophobic-hydrophilic interactions between (co)polymer and water. The temperature at which the phase separation occurs is called cloud point temperature (Tc). According to the phase transition behavior, there are primarily two categories of thermosensitive (co)polymers.

(a) LCST-type (co)polymers As illustrated in Scheme I.1, the first family concerns (co)polymer for which the phase diagram exhibits a transition from a monophasic to a biphasic region upon heating. This type of (co)polymers possesses a good solubility in water at low temperature because of hydrogen bonds between water molecules and polar groups of (co)polymers. As temperature increases, these hydrogen bonds are broken, water is released and intra-and intermolecular interactions between the (co)polymer chains become stronger, which induces the formation of aggregates and results in cloudy solution. The minimum temperature on the separation curve is called lower critical solution temperature (LCST). Strictly speaking, the LCST is not equal to Tc since LCST is the minimum value of Tc in the full phase diagram while Tc refers to the temperature at which the system changes from one-phase to two-phase state at a fixed (co)polymer concentration. It is therefore important to pay attention to the concentration-dependent Tc when comparing results issued from the literature. In this thesis, Tc refers to phase transition temperature of thermoresponsive (co)polymers measured at a given concentration.

The most extensively reported LCST-type homopolymers with different Tc values are summarized in Table I ethoxy) ethoxy) ethoxy) ethoxy) ethyl methacrylate), PDEGMA: poly(di(ethylene glycol) methyl ether methacrylate), PTEGMA: poly(tri(ethylene glycol) methyl ether methacrylate), PPEGMA: poly(penta(ethylene glycol) methyl ether methacrylate), PTEGA: poly(tri(ethylene glycol) methyl ether acrylate), POEGA: poly(oligoethylene oxide) acrylate), PTEGEMA: poly(tri(ethylene glycol) ethyl ether methacrylate), PDEGA: poly(di(ethylene glycol) ethyl ether acrylate), PTEGEA: poly(ethoxytri(ethylene glycol) acrylate), PMDEGA: poly(methoxy diethylene glycol acrylate), PVCL: poly(N-vinyl caprolactam), PVPip: poly(Nvinylpiperidone), PNVBA: poly(N-vinyl-n-butyramide), PNVIBA: poly(N-vinylisobutyramide).

(b) UCST-type (co)polymers

The second family of thermorespnsive (co)polymers exhibits a transition from a biphasic to a monophasic region in the phase diagram upon heating (Scheme I.2). The maximum temperature on the separation curve is called upper critical solution temperature (UCST). UCST-type (co)polymers at low temperature generally involve inter-and/or intramolecular interactions between or within different (co)polymer chains.

Therefore, this family of (co)polymers is immiscible with solvent. With an increase of temperature, these inter-and/or intramolecular interactions are broken, accompanied with enhanced hydrogen bonds between (co)polymer chains and solvent molecules.

This causes an increased solubility in the chosen solvent and the system becomes a monophasic solution.

Scheme I. 2 Phase diagram of thermoresponsive (co)polymers with UCST behavior.

Interestingly, the solvent plays a key role in studying solution behavior of thermoresponsive (co)polymers. Some (co)polymers, such as PNIPAM [30] and poly((oligo(ethylene glycol) methyl ether methacrylate)-co-(oligo(ethylene glycol) phenyl ether acrylate)) (P(OEGMEA-co-OEGPhEA)) [31] display typical LCST and UCST behaviors in different solvents.

In this chapter, we mainly focus on thermoresponsive (co)polymers with LCST behaviors, readers who are interested in UCST-type (co)polymers can refer to Table I. 2 where typical UCST-type homopolymers and their transition points are listed.

Table I.2 UCST-type homopolymers and their corresponding phase transition/clarification temperatures (TCL) a . PNIPAM TCL: 22 o C (d8-[C2mIm + ][TFSA -]) [30] PNAGA TCL: ~20 o C (H2O) [32][33][34] PNAAAM TCL: 24.3 o C (H2O) [35] PCNPCAVCP TCL: ~67 o C (mixture of ethanol and H2O) [36] PtBMA TCL: 35 o C (methanol) [37] PDEGMA TCL: 20.6/33.3 o C (ethanol/isopropanol) [38] POEGMEA TCL: 35.7 o C (isopropanol) [31,39] PAEEO2MA TCL: 26 o C (methanol) [40] PAEEO3MA TCL: 16.2 o C (methanol) [40] PAEEO4MA TCL: 4.5 o C (methanol) [40] PVEA TCL: 36.8 o C (isopropanol) [38] a TCL for UCST-type (co)polymers is temperature where solution changes from cloudy to transparent state. Abbreviations: PNAGA: poly(N-acryloylglycinamide), PNAAAM: poly(Nacryloylasparaginamide), PCNPCAVCP: poly(1-cyano-N-propylcarboxyamido vinyl cyclopropane), PtBMA: poly(tert-butyl methacrylate), PDEGMA: poly(oligo(ethylene glycol) methyl ether methacrylate), POEGMEA: poly(oligo(ethylene glycol) methyl ether acrylate), PAEEO2MA: poly ( Ref. [41] Ideally, the demixing (aggregation, dehydration) and remixing (dissolution, hydration) of thermoresponsive (co)polymers should appear at the same temperature.

However, a thermal hysteresis, difference in phase transition points in heating-cooling cycles, is commonly observed in turbidimetry measurements, such as in the cases of PNIPAM (Figure I.1B), [41] poly(N-isopropylacrylamide)-block-poly(ethylene oxide)-block-poly(N-isopropylacrylamide) (PNIPAM-b-PEO-b-PNIPAM), [42] poly(Nisopropylacrylamide)-block-poly(n-butyl acrylate)-block-poly(N-isopropylacrylamide) (PNIPAM-b-PBA-b-PNIPAM), [43] PBA-b-PNIPAM, [43] PBA-stat-PNIPAM [34] and poly((N-isopropylacrylamide)-co- (3-(trimethoxysilyl) propyl methacrylate))

(P(NIPAM-co-TMSPMA)). [44] This phenomenon can be ascribed to the difficulty to rehydrate compact aggregates formed at high temperature due to intra-chain entanglement or limited diffusion of water molecules into hydrophobic aggregates.

Only when sufficiently equilibrium time or a very low heating/cooling rate is applied, the same Tc in heating-cooling processes can be obtained. To limit this kinetic effect, Tc can be plotted as a function of heating or cooling rate and the value extrapolated to 0 °C• min -1 can be taken as the value of Tc.

(ii) Dynamic Light Scattering (DLS)

The presence of aggregates in solution results in a scattering phenomenon when this solution is irradiated with light. The intensity of scattered light is proportional to DH 6 (DH: Hydrodynamic diameter). DLS enables to measure the scattered intensity and from this to evaluate particle size and size distribution (i.e. intensity-, number-and volume-distributed diameter) at a specific temperature.

DLS results for LCST-type (co)polymers generally show small DH at temperature below Tc and large DH above Tc due to the aggregation of thermoresponsive chains upon heating. Additionally, the evolution of scattered intensity or size as a function of temperature enables to estimate Tc (Figure I.2). By using this method, poly(di(ethylene oxide) methyl ether methacrylate) (PDEGMA) was reported with Tc at 27. Ref. [45] (iii) Differential Scanning Calorimetry (DSC)

Thermal phase transition is accompanied with exchange of energy, which can be detected by DSC experiments. Tc is evaluated upon heating/cooling at onset temperature or at temperature where maximum of measured peak occurs (Figure I.3A).

In addition, the area of observed peak is equal to the variation of enthalpy (ΔH) which is regarded as the energy involved in this transition to break hydrogen bonds between water and (co)polymer chains. [48] The endothermic peak significantly relies on sample concentration (Figure I.3B), it shifts to higher temperature and its peak shape becomes broader as (co)polymer concentration decreases. It is noteworthy that a very low concentration is detrimental to Tc determination whatever onset or maximum peak temperature selected due to the poor sensibility of this technique. Ref. [48,49] (iv) Nuclear Magnetic Resonance (NMR)

Upon heating, modification of interactions occurs in solution between the (co)polymer and the solvent that results in a decreasing solubility of (co)polymer.

Therefore, thermal transition can be studied by NMR spectra by monitoring the changes in intensity and/or integration of characteristic peaks. In some extreme cases, no signals of thermoresponsive units can be detected when temperature rises over Tc. Through variable temperature 1 H NMR spectra, Tc of thermoresponsive (co)polymers can be calculated by plotting intensity or integration area of thermosensitive groups as a function of temperature, the signal intensity at a given temperature depends on the degree of mobility of observed nuclei within aggregates as depicted in Ref. [50] In addition, to efficiently study the thermoresponsiveness, spin-lattice (T1) or spinspin (T2) relaxation time can be measured since both are sensitive to changes in mobility of (co)polymer chains and solvent upon heating. Generally, for thermoresponsive groups, T2 changes slightly along with temperature since the mobility of these groups is reduced due to hydrogen bonds at low temperature and is restricted by hydrophobic association among (co)polymer chains at high temperature. For water (HDO protons or D2O deuterons), T2 reflects water behavior and (co)polymer-water interaction upon heating. In the cases of PNIPAM, [51] PNIPMAM, [51] poly(2-isopropyl-2-oxazoline) (PIPOx), [52] PVCL, [53] poly(vinyl methyl ether) (PVME) [54,55] and PEO-b-PNIPAM, [56] T2 of HDO at low temperature is higher than the value at high temperature, which is ascribed to a small portion of HDO with restricted mobility confined within aggregation structure at temperature above Tc, the water releasing from inside of the aggregates makes T2 increase over time, as shown in Ref. [50,51] Interestingly, in the cases of poly(2-ethyl-2-oxazoline) (PEOx), [57] PHPMAm53b-PDEGMA78, [50] poly(2-ethyl-2-oxazoline)-b-poly(2-methyl-2-oxazoline) (PEOxb-PMeOx), [52] PIPOx86-b-PMeOx14 [52] and Y-shape PEO44-b-PEOx252-b-(poly(εcaprolactone)87)2 (PEO44-b-PEOx252-b-(PCL87)2), [58] two T2 values were measured corresponding to the existence of two types of water at elevated temperature (see

Figure I.6):

one is related to free water with long T2 corresponding to the water in solution and the other is related to "bound" water with short T2 corresponding to the water inside of aggregates. What's more, the exchange between "free" and "bound" water molecules is slow and both can keep their stabilities for a long time. Ref. [50] (v) Fourier Transform Infrared (FTIR) Spectroscopy FTIR spectroscopy is a powerful tool to visualize changes in hydration state of individual groups upon heating since it is highly sensitive to the conformational change of thermoresponsive chains and to local environment of molecules and interaction between molecules. For instance, C=O stretching vibration of PNIPAM is observed at 1625 cm -1 corresponding to the hydrogen bonds between C=O and water at low temperature and shifts to 1650 cm -1 at high temperature due to the formation of C=O•••H-N among PNIPAM chains. Therefore, the IR difference spectra calculated by subtracting IR spectrum at temperature below Tc from spectrum at temperature above Tc reflects the conformation and interaction changes in the system. Meanwhile, pairs of negative (representing absorption at low temperature) and positive (representing absorption at high temperature) peaks of these special groups appear in IR difference spectra (see Figure I.7B). To avoid the effect of baseline drift, the difference in ΔA at ν1 (wavenumbers at positive peak) and ν2 (wavenumbers at negative peak) instead of ΔAT-T0 at ν1 or ν2 is generally utilized to follow the phase transition behavior (Figure

I.7C

) and it is defined as:

ΔΔAT-T0(ν1-ν2) = ΔAT-T0(at ν1) -ΔAT-T0(at ν2)

Where T and T0 are high and low temperatures, respectively. By using this evaluation method, Yasushi Maeda and co-workers have obtained Tc values of a series of thermoresponsive homopolymers and copolymers, such as PNIPAM, [59] poly(N,Ndimethylacrylamide) (PDMAm), [60] PNnPAM, [61] poly(N-cyclopropylamide) (PcPA), [61] PVCL, [62] poly(N-n-propylmethacrylamide) (PnPMA), [63] PNIPMAM, [63] poly(N,N-bis(2-methoxyethyl) acrylamide) (PbMoEA), [64] PDEGMA, [65] poly(N-(2-ethoxyethyl) acrylamide) (PEoEA), [66] poly(N-(2ethoxyethyl) methacrylamide) (PEoEMA), [66] poly(N-tetrahydrofurfurylacrylamide) (PTHFA), [67] poly(N-tetrahydrofurfurylmethacrylamide) (PTHFMA), [67] poly((Nisopropylacrylamide)-co-(acrylonitrile)) (P(NIPAM-co-AN20)), [68] poly((Nisopropylacrylamide)-co-(acrylamide) (P(NIPAM-co-AAm)), [68] poly (3-dimethyl(methacryloyloxyethyl) ammonium propane sulfonate)-b-poly(N,N'-diethylacrylamide) (PdMMAEAPS-b-PDEAM), [69] poly((N-isopropylacrylamide)co-(methyl acrylate)) (P(NIPAM-co-MA)), [70] poly((N-isopropylacrylamide)-co-(vinyl acetate)) (P(NIPAM-co-VAc)), [70] poly((N-isopropylacrylamide)-co-(acrylic acid)) (P(NIPAM-co-AA5)) [71] and (P(DEAM-co-AA5)). [71] Copyright 2000. Reproduced with permission from the American Chemical Society. Ref. [59] It is noteworthy that D2O is usually used as solvent instead of H2O in IR spectra measurement to avoid overlapping the water band (~1200 and 1640 cm -1 for D2O and H2O bands, respectively) with C=O stretching band (1600 cm -1 ). Consequently, a higher Tc in D2O than that in H2O is obtained since hydrogen bonds formed from D2O and (co)polymer chains are stronger than ones from H2O.

I.2.2 Main parameters affecting Tc of (co)polymers

Finely tuning Tc is a key point to broaden the potential applications of thermoresponsive (co)polymers. In the literature, factors affecting Tc value have been reported, such as molecular weight, (co)polymer concentration, topology structure, incorporated comonomers, terminal groups, additives, etc. Here, we make a summary on how these impacts influence Tc of thermoresponsive (co)polymers in aqueous solution.

(i) Effect of molecular weight Demixing point temperature of most thermoresponsive (co)polymers decreases with both increasing (co)polymer chain length and concentration. Typical examples are PDMAEMA, [17] PDEGMA, [72] poly(N-isopropyl-N-methylacrylamide) (PiPMAm), [73] PMEMA, [17] PEMAEEOMA, [18] PNAGME [13] and PVCL. [27,74] In these cases, a clear decreasing trend of Tc is detected with increasing molecular weight.

Numerous efforts have been made to explore the relationship between Tc and molecular weight for PNIPAM homopolymers due to its extensive applications.

However, this issue is still controversial. Stöver, Winnik and Nystrom have reported Tc of PNIPAM declines with an increase of molecular weight. In their work, PNIPAM homopolymers are ended with 2-propionamide, [75] ethyl 2-propionate, [75,76] methyl 2-propionate, [77] phenyl 2-propionamide, [75] hydroxyethyl, [78] propargyl [78] and chloroethyl groups. [78] On the contrary, an increasing trend of Tc along with molecular weight has been reported by Warr and co-workers. In their work, Tc of dodecyl terminated PNIPAM increases from 14 to 33 o C as its corresponding molecular weight rises from 1110 to 7170 g•mol -1 , [79] This phenomenon is also observed in PNIPAM terminated with n-hexyl [78] and N-triphenylmethyl 4-cyanovaleramide [80] groups in lower molecular weight range, after which Tc remains at a constant value and is not influenced by increasing molecular weight. Therefore, these different results on the relationship between Tc and molecular weight for PNIPAM homopolymer might be ascribed to the effect of end groups introduced in the synthesis, the detailed information of effect of end groups on Tc will be described in Section I.2.2 (v).

(ii) Effect of (co)polymer concentration PNIPAM, [76,81,82] PNASME170, [12] PNIPMAM, [2] PDEAEAM, [15] PNAEAA113 [11] and PEMAEEOMA108 [18] are reported to have lower Tc in concentrated solution than that in dilute solution: the density of (co)polymer chains in concentrated solution is high, which results in stronger hydrophobic intra-and interactions among (co)polymer chains at low temperature, although hydrogen bonds between water and (co)polymer chains dominate the system. Once temperature is raised, the hydrogen bonds in such conditions are easy to broke. Therefore, the thermal phase transition tends to take place at lower temperature. However, the intensity of concentration effect is less remarkable when concentration goes up to a critical value. of PNAGME177 starts to be independent on concentration change as concentration increases above 1 wt.%. [13] (iii) Effect of additives Considerable efforts have been taken into understanding the effect of additives (salts, organic solvents, surfactants, etc.) on Tc of thermoresponsive (co)polymers in water. The concepts of "salting in" effect (hydration) and "salting out" effect (dehydration) are proposed to analyze how salts influence Tc of thermoresponsive (co)polymer solution. Moreover, the influence of salts through their anions and cations and the amplitude of salt effect not only relate to the salt concentration, but also follow Hofmeister series, anions: [83,84] Generally, hydrated capacity of ions decreases along these two series, ions on the left displaying "salting out" effect tends to lower Tc, while right ones showing "salting in" effect shifts Tc towards higher temperature. What's more, the anion effect within Hofmeister series is more pronounced than cations. With the guideline of Hofmeister series, the salt effect (especially the anions effect) on solubility behavior of thermoresponsive (co)polymers, such as PNIPAM, [85,86] PNIPAM-b-PEO-b-PNIPAM, [42] PNASME170, [12] PNAEAA193, [11] PPO, [48] polymer based on oligo-2-ethyl-2-oxazoline side chains and a methacrylate backbone (POEtOxMA),

CO3 2-> SO4 2-> S2O3 2-> H2PO4 -> F -> Cl -> Br -~ NO3 -> I -> ClO4 -> SCN -; cations: Ba + > Zn + > Mg 2+ > Ca 2+ > Li + > Na + > Rb + > Cs + > NH4 + > N(CH3)4 + .
[87] P(DEGMA81-stat-OEOMA19) [45] and P(DEGMA80.5-grad-OEOMA19. water rather than with PNIPAM, the formation of organic solvent-water mixture reduces the hydrogen bonds formed between water and PNIPAM and leads to a decrease of enthalpy of LCST transition. To be specific, upon continuous addition of cosolvents, more water molecules are needed to form solvent-water mixture, which causes less free water are available to form hydrogen bonds between water and

(co)polymers. The remaining free cosolvent molecules can bind to (co)polymer since hydrogen bonds are formed between PNIPAM and methanol (providing hydroxyl groups) or between PNIPAM and acetone (providing carbonyl groups), which helps to improve the solubility of PNIPAM. Therefore, an increasing Tc is observed at high concentration of methanol and acetone. [90] The similar phenomenon is also observed in the cases of PNIPAM in H2O-THF and H2O-dioxane systems. [91] However, an unexpected UCST behavior occurred at higher concentration of organic solvents in the mixtures of water and ethanol (or methanol or propanol or DMSO or DMF), as shown in Figure I.8B. [90,92] due to the large hydrophobic groups, hydrophobic interactions among non-polar groups in system overweight hydrogen bonds between PNIPAM and organic solvents. Thus, a UCST behavior occurs.

Thermoresponsive homopolymer

Incorporated hydrophilic comonomer

Incorporated hydrophobic comonomer

PNIPAM DMAm, [93][94][95] ACMP, [96] MAAm, [96] MVA, [96] NVA, [96] VPL, [96] HIPAAm, [97], AAm, [94,96] HMAAm, [98] HEAAm [99] MASE, [100] BA, [101] Ac-6ACA, [102] CL, [103] HEMA, [94] VL [1] PVCL MVA, [104] NVA, [104] VP, [47,[105][106][107] VOH [108] VAc, [104] VPi, [104] HA [47] PDEGA DMAm [23 PNIPAM ended with five groups deriving from initiators with variable polarities.

The effect of termini on Tc at low molecular weight (3000 g•mol Additionally, Tc is also influenced by the number of end groups. Tc of P(NIPAM-stat-DMAm) terminated with one hydrophobic dodecyl group is detected at 46 o C, one more dodecyl group can reduce Tc to 30 o C. [113] In the case of PNIPAM, two octadecyl end groups can dramatically drop Tc by 6.7 o C compared to the unmodified PNIPAM. [82] As evidenced by these examples, the modification of thermoresponsive (co)polymer chain termini shows a similar effect on Tc as the effect of incorporation of hydrophilic/hydrophobic comonomers on Tc. In details, the thermoresponsive (co)polymers ended with hydrophilic groups tend to possess higher solvation and mobility, which results in a higher Tc, whereas the hydrophobic end groups are prone to lower Tc. Moreover, the magnitude of these effects relies on the nature of terminals.

(vi) Effect of topological structure Taking advantage of controlled polymerization techniques, a great number of (co)polymers with different topologies, such as star, branched, dendritic and cyclic typed structures, are designed and successfully synthesized, these different topologies strongly affect the bulk and solution properties (glass transition temperature, thermal phase transition, micellization, etc.). Investigation on topological effect on Tc of thermoresponsive (co)polymers allows us to gain a deep insight into modulation the complex thermoresponsiveness and to exploit better performing (co)polymeric materials.

Cyclic (also called ring) (co)polymers, compared to the linear counterparts, have no free chain ends in the (co)polymer backbone. Generally, the cyclic thermoresponsive (co)polymers exhibit lower Tc than linear ones at the same molecular weight and concentration, which was detected in the cases of PNIPAM, [114,115] PDEAm [116] and PVCL. [117] This phenomenon can be explained by the existence of steric constraints especially in smaller rings, compared to the linear (co)polymers, cyclic ones are restricted in the ring and less stretched in dimensions, which favors the interaction hydrogen bonds between cyclic (co)polymer units instead of interactions between water and (co)polymer chains, that is to say, the water molecules bound to the (co)polymer chains are easy to release with rising temperature. In addition, the number of hydrogen bonds formed between water and (co)polymer chains inside of the ring is less than those formed outside, which leads to a gradual dehydration in a broader temperature range.

However, there are some exceptions of cyclic (co)polymers with enhanced Tc values than linear counterparts. For instance, the cyclic (co)polymers of PBA-b-PEO, [118] PDMAEMA, [119] PIPOx, [120] poly((N-isopropylamide)-co-(Nacryloylhomocysteine thiolactone)) P(NIPAM-co-ATL) [121] and poly((Nisopropylamide)-co-(N-acryloylhomocysteinethiolactone))-graf-(diethylethylenediamine) /(poly(ethylene glycol) methyl ether acrylate) (P(NIPAM-co-ATL)-graf-DEDA/PEGA) [121] were observed with elevated Tc compared to their corresponding analogues. Feng and co-workers found cyclic, diblock and triblock copolymer composing of poly(2-(diethylamino) ethyl methacrylate) (PDEAEMA) and PEO blocks follow a Tc decreasing order: Tc,cyclic > Tc,diblock > Tc,triblock. [122] These phenomena may be related to the repulsive force between the rings or cyclic grafts. Winnik reported cyclic PNIPAM shows higher Tc than the linear analogue under the similar molecular weight and concentration, [123] the possible explanation is the introduction of different groups in synthesis of polymer, the effect of chain termini on Tc of linear polymers is believed more crucial than that of cyclic analogues.

Star (co)polymers basically are composed of one core and a certain number of arms in structure. The limited space near or in the core region restricts dispersion of water molecules. The hydrogen bonds formed between water and (co)polymer chains are relatively less, and they are broken more easily upon heating, therefore, the Tc of such thermoresponsive (co)polymers tends to be lower than linear counterparts at the same molecular weight and concentration. This explanation is evidenced by the case of star typed PDEAM. [116,124] What's more, in the cases where molecular weight is sufficiently high and Tc is no longer dependent on molecular weight, such as PNASME, [125] PNIPAM [126] and PDMAEMA, [127] increasing arm numbers in star typed thermoresponsive (co)polymers means higher chain density. Compared to those analogues with less arms, the hydrophobic intra-interaction in the core region become very strong with increasing temperature. Therefore, the corresponding Tc values are detected at lower temperature. PNnPAM84-b-PEMAM42 (1) Tc < TCL. In this case, copolymers are soluble at temperature below Tc and at temperature above TCL, and both blocks exhibit poor solubilities or precipitate in the intermediate temperature range.

(2) Tc > TCL. In this case, copolymers display an inverse behavior: they are soluble in the intermediate temperature range (TCL < T < Tc) whereas poor solubilities occur at temperature below TCL and above Tc. Typical examples of LCST-UCST typed copolymers are listed in Table I.5. (iii) Copolymers with a UCST-UCST behavior UCST-UCST typed copolymers, consisting of two individual UCST-type blocks, undergo a (double hydrophobic)-to-amphiphilic-to-(double hydrophilic) transition with increasing temperature. This behavior is opposite to that of LCST-LCST typed copolymers. Unfortunately, there are few reports of such type copolymers involving the thermoresponsive property in dilute solution (phase transition temperature and self-assembly).

I.2.4 Self-assembly of thermoresponsive (co)polymers

The self-organization behavior of amphiphilic copolymers, resulting from the inherent molecular structure, can be predicted based on a "packing parameter" of copolymer chains, p, which is calculated by the following formula,

p = ν α 0 l c
where ν is volume of hydrophilic chains, α0 is optimal area of head group and lc is length of hydrophobic tail. Scheme I.8 illustrates the relation between the value of p and the aggregate geometry. [171] Scheme I.8 Evolution of morphologies of aggregates depending on the value of packing parameter p. Copyright 2009. Reproduced with permission from the WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Ref. [171] As stated above, thermoresponsive (co)polymers usually undergo a modification of their solubility in aqueous solution in response to a change of temperature.

Depending on the microstructure of the studied (co)polymer, this modification can result in the formation/modification of aggregates. The formation of such assemblies and the effect of temperature on aggregates structure can be studied through scattering (light, neutrons, and X-ray) and microscopy measurements. Only thermoresponsive block (co)polymers are discussed in this section.

(i) Self-assembly of mono thermoresponsive (co)polymers Thermoresponsive (co)polymers in different concentration regions display various aggregation states, such as unimers, nanoparticles with spherical, worm-like micellar and vesicular geometry in dilute solution as well as sol and gel in concentrated solution.

Here, temperature-induced morphological transition will be discussed with respect to (co)polymer concentrations. The self-organization behavior of thermoresponsive triblock copolymers is more complex and is related to the copolymer specific microstructures (i.e. symmetric and asymmetric structures). For symmetric structure, according to the polarity of nonthermoresponsive block, two transitions of unimers-to-(core-corona structure) and (core-corona structure)-to-(core-shell structure) are commonly observed. In the case of triblock copolymers, bearing one thermoresponsive and two double hydrophilic blocks or one thermoresponsive and two double hydrophobic blocks, their temperaturetriggered morphological transition is similar to hydrophilic or hydrophobic modified diblock copolymers. For asymmetric triblock copolymers with different block sequences, the self-assembly behavior upon heating depends on the block order. The morphological transition of triblock copolymers with different microstructures is summarized in Table I.8.

(b) In concentrated solution

The self-assembly behavior of thermoresponsive (co)polymers in concentrated solution is basically studied in terms of macrophase transition. The detailed mechanism of thermoresponsive block (co)polymers is depicted in Scheme I.9. Scheme I.9 Schematic illustration of temperature-induced gelation for block copolymers in water via micelle packing and entanglement. A micelle is shown as a circle. Copyright 2007. Reproduced with permission from the Wiley Periodicals, Inc. Ref. [197] In concentrated solution, thermoresponsive (co)polymer are well dispersed in water either as micelles (for amphiphilic structures) or as unimers (for double hydrophilic structures). Increasing temperature leads to the formation of a three-dimensional networks with orderly arrangements, which is generally defined as transparent gel. This network result either from the packing of preexisting micelle or from the aggregation of (co)polymer. With a further increase of temperature, the size of clusters or the distance between clusters reaches the range of wavelength of visible light, the gels become opaque to eyes. Continuously increasing temperature, due to the over-hydrophobicity, the micellar network is broken with volume shrinkage by expelling water, and a macrophase separation occurs, which is noted as gel with syneresis or dehydrated gel. The temperature-induced gel via micelle packing and entanglement, should be distinguished with chemical crosslinked gel formed through covalent bonds. Indeed, the former one displays a good reversibility of sol-to-gel transition upon heating/cooling. [197] The transparent, opaque and syneresis gels are not always observed sequentially upon heating for all thermoresponsive (co)polymers. Their appearances are dependent on the degree of entanglement at a specific temperature, relating to (co)polymer composition and concentration. For instance, these three types of gel were all observed in PNIPAM38-b-PEO114 in concentration range from 5 to 7 wt.%, whereas only opaque and syneresis gels occur in PNIPAM228-b-PEO114 and PNIPAM143-b-PEO114 at the same concentration. [198] Additionally, P(BA-stat-NIPAM)21k displays three gel phases at concentration of 30 wt.% upon heating it loses transparent gel phase at 20 wt.%. What's more, only transparent gel exists at 10 wt.%, and no sol-to-gel transition is detected when concentration declines to 5 wt.%. [199] The gelation temperature can be easily tuned for a specific application by adjusting molecular weight, composition and/or architecture. [197] For instance, an increase of hydrophobic BuMA ratio in PEGMA-b-PBuMA-b-PDMAEMA drives formation temperature and concentration of transparent gel shift towards lower value. [133] Statistical copolymers of P(DMAEMA30-co-BuMA13-co-EGMA9), P(EGMA2-co-BuMA14-co-DMAEMA16), P(EGMA2-co-EtMA18-co-DMAEMA16) (EtMA: ethyl methacrylate) and P(EGMA2-co-HMA12-co-DMAEMA16) (HMA: hexyl methacrylate) cannot form gels or form gels with weak or unstable properties compared to triblock analogues at the same composition. [133,200] Additionally, the gel formed in triblock structure of poly(ethylene oxide)69-b-poly(styrene oxide)8-b-poly(ethylene oxide)69 (PEO69-b-PSO8-b-PEO69) is more difficult at low concentration than in diblock analogue of PSO10-b-PEO135. [201] (ii) Self-assembly of dual thermoresponsive (co)polymers Thermoresponsive (co)polymers comprising of two thermoresponsive blocks have two different transition temperature values. The hydrophilic/hydrophobic ratio of overall copolymers in each temperature regime is different, which drives these copolymers self-organize into different morphologies with various sizes. Although the study of such system is complex, the sensitivity and specificity are higher than that of mono-thermoresponsive (co)polymers.

(a) Self-assembly of copolymers with LCST-LCST behavior Copolymers with LCST-LCST behavior undergo a gradual dehydration with an increase of temperature. For dual thermosensitive diblock copolymers and symmetric triblock copolymers, the copolymers change from double hydrophilic (T < Tc,1) to amphiphilic (Tc,1 < T < Tc,2) to double hydrophobic (T > Tc,2) state, such copolymers tend to undergo a unimer (T < Tc,1) to core-corona aggregates (Tc,1 < T < Tc,2) to coreshell micelles or aggregate clusters (T > Tc,2) transition.

The solubility change of triblock copolymers containing an additional hydrophilic or hydrophobic block (ABC-type) is more complex. Copolymers bearing one hydrophilic block undergo (triple hydrophilic)-to-amphiphilic change upon heating, while those copolymers with one hydrophobic block exhibit amphiphilic-to-(triple hydrophobic) transition under continuously increasing temperature. Besides the hydrophilic-hydrophobic ratio at a fixed temperature, the block sequence and copolymer structure also matter morphologies as mentioned above. The typical selfassembly behavior of LCST-LCST typed copolymers trigged by temperature is summarized in Table I.9. (b) Self-assembly of copolymers with LCST-UCST behavior LCST-UCST copolymers with Tc < TCL or Tc > TCL present amphiphilic characters at lower and higher temperature and are therefore prone to display "schizophrenic" behavior via formation of two distinct core-shell structures upon temperature adjustment. In the intermediate temperature window, these copolymers are soluble or insoluble depending on the respective Tc and TCL values. This inversibility of polarity of aggregate nucleus provides insights to encapsulate and to release different compounds in solution by simply modulation of temperature. Morphological transition of LCST-UCST typed copolymers upon heating is summarized in Table I.10.

Concerning the fact that some (co)polymers in organic solvent or mixture of water and organic solvent display UCST behavior, it is worth noting the solvents selected in the cases of LCST-UCST typed copolymers. a In the cases of LCST-UCST typed triblock copolymers, the effect of non-thermoresponsive block on self-assembly is not considered.

I.3 pH-responsive (co)polymers

In the case of pH-sensitive polymers, the key element in such system is the presence of ionizable weak acidic or basic moieties attached to the hydrophobic backbone. Upon ionization, the coiled chains stretch dramatically responding to the electrostatic repulsions among generated anions or cations. However, complete ionization of polyelectrolytes is more difficult due to electrostatic effects exerted by other adjacent ionized groups. This transition between tightly coiled and expanded state is influenced by any condition that modifies electrostatic repulsion, such as ionic strength and counterions type. Consequently, it has to be kept in mind that after several cycles of protonation/deprotonation by addition of acids or bases, the accumulation of salt has a detrimental effect on the organization of (co)polymers in aqueous solution.

I.3.1 Main families of pH-responsive homopolymers

According to the functional groups, pH-responsive (co)polymers are divided into two categories: (co)polymers with acidic groups (carboxylic, sulfonic, phosphonic, boronic acid groups) and (co)polymers with basic groups (tertiary amine, morpholine, pyrrolidine, imidazole, piperazine and pyridine groups).

Polyacids

PAA pKa: 4.52-4.55 [203] PMAA pKa: 4.86 [204] PVBA pKa: 7.1 [205] PSSA pKa: 0.94 [206] PVPA pKa: 3.02 [207] Polybases PDMAEMA pKa: 7.4 [17,208] PDEAEMA pKa: 7.5 [17,208] PMEMA pKa: 4.9 [17] PDPAEMA pKa: 6.0 [17] PDEAEAM pKa* P4VP pKa: 4.4 [209] P2VP pKa: 4.5 [210] *value measured in Chapter IV. Polyacids are deionized at low pH and ionized with negative charges at neutral and high pH, while polybases have an opposite behavior, being protonated at low pH values and deprotonated at high pH. For these pH-responsive (co)polymers, it is therefore crucial to determine the acidic dissociation constant, Ka (or its negative log: pKa) to know at which pH the ionic/non-ionic transition occurs. The most extensively investigated pH-responsive homopolymers and their corresponding pKa values are summarized in Table I.11.

When both acidic and basic groups coexist within one chain, (co)polymers are defined as polyampholytes, which experience multiple protonation states in different pH regimes separated by isoelectric point (IEP). This IEP depends on the polyampholyte composition and the corresponding pKa values of acid and basic units.

At pH below IEP, due to the protonated polybase segments and deionized polyacid block, the positive charges domain the system. By contrast, at pH above IEP, it is governed by the negative charges because of deprotonation of polybase units and ionized polyacid block. At a narrow pH window around IEP, the polyampholytes tend to precipitate due to the electrostatic attraction among charged groups. I.3.2 Impacts on self-assembly of pH-responsive (co)polymers pH adjustment alters the protonation/deprotonation (or ionization/deionization) degree of pH-sensitive moieties and the electrostatic repulsion among the charged chains, which influences the hydrogen bonding network, ionic/hydrophobic interactions in the system, and further causes solubility change of (co)polymers in aqueous solution. To well understand and control the self-assembly behavior of pHresponsive (co)polymers, apart from hydrophilic/hydrophobic ratio at a specific pH, the impacts of different parameters such as pH, pH-sensitive chain length, concentration of salt and (co)polymer architecture on the aggregates shape and size should be considered.

(i) Effect of chain length of pH-responsive segment

The effect of chain length on the self-assembly of pH-responsive (co)polymers is ascribed to the ionization degree of pH-sensitive blocks. In other word, pH-sensitive segments with different chain lengths at a fixed pH imply variable ionization degrees.

Meanwhile, for those (co)polymers with identical chain length but at different pH values, their electrostatic repulsions between charged chains are variable and make the corona volume swell or deswell with pH change. Therefore, a profound change in morphology and size takes place as pH-responsive units are not completely ionized.

Once these units are totally ionized, adjusting system pH no longer exert significant (ii) Effect of ionic strength In ionized state, the addition of salt into pH-responsive (co)polymers solution tends to shield the intra-corona repulsion among the charged (co)polymer chains due to the association of salt with charged chains, this causes a change of morphology towards structure with lower curvature. For instance, poly(glycerol monomethacrlyate)50-bpoly(2-hydroxypropyl methacrylate)140 (MPETTC-PGMA50-b-PHPMA140) formed spherical micelles at pH 3 and it transformed into worm-like micelles upon addition of KCl. [214] The addition of salt has another more unexpected consequence called "salting out" effect, this term is used to describe the decreasing solubility, which results from the addition of salts or electrolytes to solute-solvent system. When salt concentration increases, some of water molecules are attracted by the salt ions, which leads to a decrease of the number of water molecules available to interact with charged part of (co)polymer. The "salting out" effect is responsible for a change of solubility of (co)polymers in aqueous solution or induces a modification of the morphology of these (co)polymer aggregates.

PMEMA is a polybase which has good solubility in neutral and acidic aqueous solution. Meanwhile, it is sensitive to the presence of electrolytes and displays "salting out" effect in presence of 0.2 -0.3 M Na2SO4 at room temperature. [17] Consequently PMEMA-based pH-responsive block copolymers (i.e. PDEAEMA34-b-PDMAEMA67b-PMEMA39, [215] PMEMA-b-PDEAEMA [216,217] and PVBA63-b-PMEMA123 [205]) exhibit "schizophrenic" behavior in response to addition of salt and pH change. As illustrated in Scheme I.10, starting from a block copolymer at pH value where both blocks are completely hydrated, the addition of salt with a sufficient high level causes the formation of micelles due to "salting out" effect of PMEMA block. Once the addition of salt is replaced with pH change, inverse micelles with a core of pH sensitive block and a shell of PMEMA block.

(iii) Effect of charge balance within the (co)polymer

The effect of charge balance within block copolymer on self-organization is remarkable in the cases of polyampholytes. pH change drives structure of PAA134-b-P2VP628-b-PAA134 transfer from unimers at pH below IEP to micelles with P2VP core and PAA corona at pH above. [218] Additionally, the multiarm star-shaped terpolymer with 9 arms, poly(styrene)9-poly(divinyl benzene)-(poly(2-vinyl-pyridine)126-bpoly(acrylic acid)69)9 ((PSt33)9-PDVB-(P2VP126-b-PAA69)9) was reported with the formation of unimolecular, worm-like and multicore micelles at lower pH range, as well as irregular multistar aggregates, network-like assemblies and compartmentalized micelles at higher pH region (Scheme I.11). [219] Scheme I.11 Chemical structure and TEM images at different pH values of star-shaped (PSt33)9-PDVB-(P2VP126-b-PAA69)9. Copyright 2011. Reproduced with permission from the Royal Society of Chemistry. Ref. [219] (iv) Effect of architecture Based on the synthetic process adopted, the architectures of pH-responsive (co)polymers can be linear, star, graft, branched and network. Depending on (co)polymer concentration and hydrophilic-hydrophobic ratio, these (co)polymers can self-assemble into unimers, micelles, vesicles and hydrogels. Changes in aggregates morphology and size of different families of pH-responsive copolymers upon pH modulation are depicted in Scheme I.12. [220] Scheme I.12 Morphological transition triggered by pH change for pH-responsive (co)polymers with (a), (b), (c), (d) linear, (e) dendrimer, (f) hyperbranched, (g) star and (h) brushes structures. Copyright 2017. Reproduced with permission from the Royal Society of Chemistry. Ref. [220] pH-induced morphological transition of linear (co)polymers (such as block, statistical, gradient, etc.) is the most extensively studied project. Except pH-triggered unimers-to-micelle, micelle-to-(reverse micelle) and vesicle-to-(reverse vesicle) transitions mentioned in Scheme I.12, the vesicle-to-cylinder-to-sphere, [221] unimersto-(mixture of micelles and micelles cluster), [222] spheres-to-(mixture of worm-like micelles and vesicles), [223] and sphere-to-vesicle [223] transitions have also been reported in the literature.

I.3.3 Dual temperature-and pH-responsive (co)polymers

The behavior of such dual thermo-and pH-responsive (co)polymers are relatively complex to study since each stimulus needs to be considered as stated above. Some pH-responsive homopolymers also possess thermoresponsive properties at a given pH depending on the degree of protonation. Such family are regarded as dual thermo-and pH-responsive homopolymers, typical examples are listed in Table I.12.

Table I.12 Thermo-and pH-responsive homopolymers.

PEMAEEOMA [18] PDPAEMA [224] PDMAEMA [127] PIMA [225] PEPyM [226] PMAME [227] PMAEE [227] PMAMP [227] PMAEP [227] PDEAEAM [15] P(MEO1-DEAE-AM) [228] P(DEAE-NIPAM-AM) [229] P(MA-iAsn-OH) [230] Abbreviations: PIMA: poly For instance, PDEAEAM and PDMAEMA homopolymers, are fully soluble at pH below pKa whatever the temperature since electrostatic repulsion among the charged chains prevent chains from aggregation upon heating. At pH above pKa, these homopolymers are thermoresponsive and behave coil-to-globule or clear-to-cloud transition with increasing temperature.

Block copolymers comprising of one thermo-responsive block and one pH-

responsive

I.4 CO2-responsive (co)polymers

CO2-responsive (co)polymers are (co)polymers that are prone to react with CO2 in aqueous solution, this reaction can be reversed upon alternate bubbling CO2/inert gases.

As a stimulus, CO2 has promising prospects due to its abundance, nonflammability, low toxicity and biocompatibility. Moreover, CO2 is easy to be removed without any accumulations or contaminations in the system upon repeated cycles. CO2responsiveness of (co)polymers is realized by incorporation of CO2-sensitive functional groups along the (co)polymer chains. The most reported CO2-responsive functional groups are organobases, such as amine, amidine, guanidine and imidazole, whose structures are shown in Scheme I.13.

Scheme I. 13 Structures of CO2-responsive groups.

I.4.1 CO2-responsive mechanism

The trigger of CO2-responsiveness is regarded as the protonation of CO2sensitive groups within (co)polymers, which changes from uncharged to positively charged state after reaction with CO2, this is similar to pH-responsive mechanism of polybases. The corresponding pKa value is an important parameter to judge the feasibility of CO2-switchability. The detailed mechanism of each CO2-sensitive group is demonstrated in Scheme I.14.

For CO2-responsive groups containing N-H bonds, such as poly(allylamine) bearing two N-H bonds, when less quantity of CO2 is added, amine groups react with CO2 to form ammonium carbamates, with increasing CO2 concentration in the system, carbamates then hydrolyze into bicarbonate salt. These two products can be distinguished by signals in 13 C NMR spectra where characteristic peaks at 165 and 160 ppm are attributed to carbamate and bicarbonate, respectively. [241] When bulky groups are attached to nitrogen atom in amine groups, the carbamate formation is restricted due to the steric effect, hence, bicarbonate salts are more readily to generate. For CO2-responsive groups without N-H bonds, like tertiary amines, amidines, guanidines and imidazoles, they typically react with CO2 to form bicarbonate salts instead of carbamates. In general, tertiary amines have pKa around 6.5 -8.0, the protonation/deprotonation by gas treatment is easily accessible. Moreover, monomers bearing tertiary amines, such as DEAEMA and DMAEMA, are commercially available.

Amidines have an average pKa value around 9.0, which provides themselves with stronger basicity and higher CO2-sensitivity as well as faster responsive speed.

Guanidine structures contain three nitrogen atoms attached to one carbon and have a pKa around 13.5. The chemical structure of imidazoles is generally regarded as cyclic amidines with a five-membered ring, alkyl substituted imidazoles possess higher pKa values of 10 -14.5. Due to the higher pKa values of guanidines and imidazoles, inverting bicarbonate salts to neutral states by aeration inertial gases to remove CO2 is not efficient, a common approach is heating the aqueous solution. [242,243] I.4.2 Self-assembly behavior of CO2-responisve (co)polymers

The solubility of CO2-responsive (co)polymers in aqueous solution is significantly influenced by the protonation/deprotonation upon CO2 treatment/removal. Due to the shift of hydrophilic/hydrophobic balance in the system, these (co)polymers can assemble into different aggregates with variable geometries and sizes. In addition, the impacts of (co)polymer architecture, block sequence and (co)polymer composition should also be taken into account during the analysis of aggregation of (co)polymer.

Table I. 14 summarizes some examples of CO2-induced morphological transition. Table I. 15 Homopolymers with dual thermo-and CO2-responsive properties.

PDEAEAM [15] PEPyM [16] PDMAEMA [137] P(DEAE-NIPAM-AM) [229] P(MEO1-DEAE-AM) [228] PMAEE [227] PIMA [225] PEMAEEOMA [18] Table I. 16 Examples of temperature-and CO2-switchable morphological transition. Regarding the relative tedious synthetic routes of such multi-responsive monomers (and their corresponding homopolymers) and the access to obtain aggregates with different structures and morphologies, many studies have been reported the combination of thermoresponsive units and CO2-responsive moieties in (co)polymers with different structures via controlled radical polymerization. Some examples of temperature-and CO2-tuned self-assemblies are presented in Table I. 16. It is noteworthy that analysis of responsiveness in presence of CO2 at high temperature should be taken care since CO2 is not stable in aqueous solution at relatively high temperature, which influences the protonation degree of CO2-responsive units to a certain extent.

I.5 Synthetic methods to prepare multi-stimuli (co)polymers

The precise synthesis of well-defined (co)polymers is a prerequisite to achieve desired properties, such as precisely tuning Tc values over a broad temperature range or controlling self-assembly behaviors triggered by external stimuli. To achieve such goal, controlled radical polymerization methods such as nitroxide-mediated radical polymerization (NMP), [259] atom transfer radical polymerization (ATRP), [260] reversible addition-fragmentation chain transfer (RAFT) polymerization [261][262][263] are the tools of choice. Indeed, the rapid development of controlled radical polymerization provides insights to design and synthesize (co)polymers with controlled molecular weight, narrow polydispersity and advanced microstructure. Thanks to these sophisticated techniques and post-polymerization modification, a great number of multi-stimuli responsive (co)polymers have been synthesized. In this section, we primarily make a short introduction on the synthesis of stimuli-responsive (co)polymers by using RAFT polymerization and/or ATRP since these two methods have been extensively reported in the literature.

I.5.1 RAFT polymerization

RAFT polymerization is an effective and versatile method to synthesize (co)polymers with controlled structures and compositions through a reversible chain transfer process, in which the number of radicals and occurrence of termination reactions are reduced to achieve (co)polymer chains with controlled growth. In a typical RAFT polymerization, three important components are included: monomer, initiator and RAFT agent (or chain transfer agent). Scheme I. 15 depicts key steps of chain transfer and main equilibria processes in RAFT polymerization, the initiation and termination steps are similar to free radical polymerization, and they are not discussed here. In pre-equilibrium step, initial RAFT agent reacts with reactive radicals (propagating radicals) to yield a macro-RAFT agent (or dormant species), which further exchanges functionality with reactive radicals in main equilibrium step to form a new macro-RAFT agent, whose polymerization degree is different from the one's in preequilibrium step.

Scheme I. 15 Chain transfer and main equilibria in RAFT polymerization mechanism.

Synthesis of multi-stimuli responsive block copolymers by RAFT polymerization basically includes at least two consecutive controlled radical procedures. In each step, the chosen RAFT agent should be able to effectively mediate the controlled polymerization of different monomers. Therefore, a key point in RAFT polymerization is the selection of RAFT agent, whose effectiveness is determined by the nature of activating and leaving groups. Additionally, some properties of synthesized (co)polymers may be influenced by the residual groups of RAFT agents as end groups attaching to the (co)polymer main chains. For instance, the polarity of end groups influences Tc of synthesized thermoresponsive (co)polymers and their colloidal properties in water. [75,214,264] All in all, RAFT polymerization has been successfully and extensively employed in synthesis of multi-stimuli responsive (co)polymers due to its unique advantages: (1) good compatibility over a wide range of monomers; (2) mild polymerization conditions.

Table I. 17 gives some examples of stimuli-responsive (co)polymers synthesized by RAFT polymerization.

P(mPEGV)32-b-PNIPAM170-b-PSt166 Dual temperature (LCST-LCST) EMP ACPA(AIBN) [148] PNIPAM54-b-PDMAEMA46-b-PSt460 Dual temperature (LCST-LCST) CDTPA AIBN [149] PNASME170-b-PNIPAM63 Dual temperature (LCST-LCST) DMAT AIBN [12] PNIPAM115-b-PNAEAA230 Dual temperature (LCST-LCST) ECT AIBN [11] PDEAEMA-b-PNIPAM Temperature, pH CEP V-501(VA-044) [234] PDMA-b-PDEAEMA CO2 CPDB AIBN [244] PDEAEMA60-b-PNIPAM40 Temperature, CO2 DMP AIBN [254] PEO113-b-PHFBMA110-b- PDEAEMA212 CO2 macro PEO ACPA [251] PEO45-b-P(DEAEMA90-co-St66) CO2 macro PEO45 ACVA [245] PEO45-b-PDEAEMA93-b-PSt66 CO2 macro PEO45 ACVA PEO113- b-P(4VP90-co-DEAEMA30) CO2 macro PEO113 ACVA [249] POEGMA33-b-PBzMA400-b- PDEAEMA100 CO2 CPADB AIBN [253] PEO-b-P(AAm-co-AN)-b-PDEAMA Temperature (UCST), CO2 macro PEO45 AIBN [258]
a Only RAFT agent and initiator are presented, other polymerization conditions like solvents, polymerization temperature, reaction time and post-modification can be referred to the corresponding references.

I.5.2 ATRP

ATRP is a catalytic process involving a transition-metal complex to create equilibria between growing and dormant radicals. As illustrated in Scheme I.16, an ATRP system primarily consists of monomer (M), alkyl halide initiator and transitionmetal catalyst (Mt). The polymerization reaction is usually initiated by the latter two components. In details, the catalyst can activate alkyl halide initiator (dormant species) via a transfer of halide atom, leading to the formation of reactive radicals (Pn•), which reacts with monomer to extend (co)polymer chains (Pn-X). Meanwhile, these reactive radicals are deactivated and become dormant species by transferring a halide atom from Mt z+1 -X. This reversible step can be adjusted to reduce concentration of dormant species and to minimize termination reaction as well as to realize (co)polymer chains with controlled grow. [260] Scheme I. 16 Reversible activation/deactivation in ATRP mechanism.

Table I. 18 Some examples of stimuli-responsive (co)polymers synthesized through ATRP reaction.

(Co)polymer Stimulus type Experimental conditions a

Ref.

Catalyst Initiator

PNIPAM450-b-P(NIPAM244-co- HMAAm70) Dual temperature (LCST-LCST) CuBr/Me6TREN EBB [98] PEO45-b-PNIPAM380-b- P(NIPAM423-co-HEAAm42) Dual temperature (LCST-LCST) CuCl/Me6TREN PEO45-Br [152] PEO-b-PSt-b-PDEAEMA CO2 CuBr/PMDETA (CuCl/CuCl2/PMDETA) PEO-Br [252] PEO-b-P(DEAEMA-co-CMA) CO2 CuBr/PMDETA PEO-Br [244] P(DEGMA180-co-DMAEMA38)- b-PEO455-b-P(DEGMA180-co- DMAEMA38)
Temperature, CO2 CuCl/PMDETA Br-PEO-Br ATRP has appealing characters, such as good tolerance over a wide range of functional monomers, readily mono-and multi-functionalized initiators and concurrent growth of all chains. However, some limitations should be noted: (1) the final obtained (co)polymers typically contain a small amount of residual metal, which may influence the applications, (2) transition-metal catalysts at lower state are easy to be oxidized.

Some examples of stimuli-responsive (co)polymers synthesized via ATRP are summarized in Table I.18.

I.5.3 Other methods

In addition to these two synthetic methods mentioned above, other methods, such

I.6 Applications

Multi-stimuli responsive (co)polymers are one kinds of smart materials and have attracted great interest in recent years. Due to their physiochemical property change (such as solubility, chain conformation, dimension, configuration…) in response to the subtle external environment change, these (co)polymers can be used as drug carriers, functionalized surface and sensors, etc. in the potential fields of biotechnology, nanotechnology, functional membranes and smart coatings.

I.6.1 Drug carrier Self-organization and particle size are the most important parameters to realize controlled drug delivery and release. As stated above, the morphology of stimuliresponsive (co)polymers can be triggered by specific stimuli, which provides possibilities on design of stimuli-sensitive materials as drug carriers with regard to the problems of solubility, enzymatic degradation and non-toxicity of drugs. These intelligent carriers can be designed with micelle or vesicle or hydrogel structures to load drugs, to reduce the side effects and to maximize the efficiency of drugs (Scheme I.17). [272] Scheme I.17. Schematic representation of stimuli-responsive (co)polymers used for drug delivery and controlled release.

Since hydrophobic micelle core can associate some lipophilic drugs, the highly hydrated corona provides stabilizing interface between hydrophobic cores and aqueous solution, which helps to improve the dispersion of micelles and to suppress the intermicellar aggregation. Once the external environment changes, the micellar structure is destabilized and drives drug diffuse out quickly from the micelle cores. [174,273] Additionally, vesicular structures have high loading capacity, the hydrophilic drugs can be placed inside of vesicles while the hydrophobic molecules are integrated into bilayer, as stimuli applied, vesicular structures dissociate and drugs are released. [274] Meanwhile, internal space in 3D network structure endows hydrogels with high efficiency to encapsulate and release drugs via volume compaction and expansion, which can be modulated by external stimuli. [275] I.6.2 Functionalized surface Metal nanoparticles, such as gold and silver nanoparticles (AuNPs and AgNPs), have obtained ever-increasing interest due to their unique properties and extensive applications as smart sensors. However, bare metal nanoparticles undergo aggregation in response to a subtle change of ionic strength or pH in system. Hence, the stabilization of such particles in solution is required to use some stabilizing agent such as (co)polymer. These hybrid materials can be obtained through different strategies (in situ formation, ligand exchange, "grafting from" or "grafting to" strategies). In addition, modification of stimuli-responsive (co)polymers to metal NPs surface confers to the obtained hybrid materials with specific additional properties. Indeed, such obtained hybrid nanoparticles not only keep the unique properties of bare nanoparticles (such as optical, catalytic properties…), but also own the special properties of (co)polymers, especially the stimuli-responsiveness and processibility. For instance, the system stability of coating PNIPAM10k on AuNPs at room temperature is improved over a broad pH range (1-13) and high ionic strength (up to 1 wt.%). And its catalytic efficiency in reduction of p-nitrophenol to p-aminophenol is influenced by temperature change due to the thermoresponsive PNIPAM, the reaction rate increases along with temperature until Tc reaches, which is followed by a decreasing tendency. [276] Additionally, AgNPs coated with CO2-responsive PDEAEMA has a reversible dispersion/aggregation transition in water upon CO2 treatment/removal, and its catalytic activity after bubbling CO2 is higher in reduction of p-nitrophenol to paminophenol than that in absence of CO2 (Scheme I.18).

I.7 Conclusions

The latest development of multi-stimuli (thermo-, pH-and CO2-) responsive (co)polymers is reviewed in this chapter. Some (co)polymer molecular parameters

II.1 Introduction

Metal nanoparticles, [1] especially gold nanoparticles (AuNPs), have attracted much attention because of their unique electronic, optical and catalytic properties resulting in their wide applications ranging from optoelectronics to biology. [2,3] These properties strongly depend on the particle size and shape, the nature of the protecting organic shell and the interparticle distance. [4] AuNPs are colloidally unstable and are susceptible to irreversible aggregation, but they can be stablized through the grafting or adsorption of small organic molecules such as citrates, surfactants, ligands or polymers. These organic molecules provide an additional tool to modulate physicochemical properties. To this end, polymers have proved to be ideal material of choice due to their flexibility for tailoring specific uses and also for their greater long-term stabilizing properties compared to small molecules (such as citrates). Notable examples include responsive polymers. Indeed, coating AuNPs with stimuli-responsive polymers is a convenient way to reversibly change the properties of AuNPs. Thermoresponsive (co)polymers with LCST-typed behavior have been grafted on AuNPs without losing their thermoresponsiveness. [5][6][7][8][9] These obtained hybrid materials not only show a steric stability, but also have a capacity to control the NPs properties (electronic, optical and catalytic properties…) in response to a change of temperature. [10][11][12] Hence different families of thermoresponsive polymers like poly(N-isopropylacrylamide), [13][14][15][16][17][18] poly(methyl vinyl ether), [19] poly(N-acryloyl-N'propyl piperazine) [20] and copolymers based on oligo(ethylene glycol) (meth)acrylate [21][22][23] or poly(N-vinyl caprolactam) (PVCL) [24,25] have been used to obtain such hybrid nanoparticles. The use of this last family is of special interest for the formation of hybrids presenting a sharp reversible response to temperature. Moreover, the cloud point temperature (Tc) of PVCL and corresponding hybrid materials can be easily tuned either by adjusting polymer chain length or by changing polymer concentration. [24] PVCL belongs to the family of poly(N-vinyl lactams) like poly(N-vinylpyrrolidone) (PVP), which is not thermoresponsive but is one of the most commonly used polymers for stabilizing NPs with different natures for diverse applications. [26] The structure of N-vinyl caprolactam properties by cobalt-mediated radical polymerization followed by a radical coupling reaction, and then studied their solution behaviors. [28,29] Hoogenboom et al. used RAFT-derived P(VCL-stat-VP) to stabilize preformed AuNPs surrounded by citrate via a "grafting to" approach. The polymer coating AuNPs showed a larger hydrodynamic size in comparison to pristine citrate@AuNPs. In presence of 0.1 M NaCl, a color change depending on the copolymer composition and Tc value of the polymer were observed. [25] The objective of this chapter is to study the influence of composition of narrowly dispersed P(VCL-stat-VP)20k copolymers with controlled molecular weight for the formation, stabilization and modulation of the properties of AuNPs. For this purpose, a series of VCL/VP statistical copolymers containing variable amounts of VP (molar content changes from 0 to 100%) was synthesized by RAFT/MADIX polymerization (MADIX standing for macromolecular design by interchange of xanthates). Then two methods (in situ formation and coating of preformed AuNPs) were used to prepare nanohybrids, whose stabilization, thermoresponsiveness and catalytic properties were investigated by transmission electronic microscopy (TEM) and UV-visible spectroscopy.

II.2 Synthesis and characterization of copolymers

The synthesis of homopolymers and copolymers of VCL and VP used in this chapter was previously performed by X. Zhao in IMRCP lab.

II.3 Formation of nanohybrids

To study the stabilization, thermoresponsiveness and catalytic properties of hybrid nanoparticles, two methods shown in Scheme II.2 were used to obtain nanohybrids: (1) in situ formation and (2) coating of preformed AuNPs.

Scheme II.2 Two synthetic pathways used for formation of nanohybrids (in situ formation and coating of preformed nanoparticles).

II.3.1 In situ formation

The first evidence of the interaction of different polymers with AuNPs is given by performing in-situ growth of AuNPs. Whereas PVP-based polymers can act as both reducing agent and stabilizer, their use as reductants lead to the formation of large particles with broad size distribution poorly adapted to catalytic applications. [30] Therefore, sodium borohydride (NaBH4) is used here as a reducing agent to have fast access to AuNPs with better control of particle size and dispersity. For this, a NaBH4 solution was added to a mixture of gold salt and concentration confirms that the presence of (co)polymer plays an important role in the control of NPs growth by interacting with the gold nuclei/gold precursor at early stage of NPs growth, which is favored on the one hand by the interactions of the thioester groups present at the end of (co)polymer chains [18] and on the other hand by the interactions of (co)polymer chain with the surface of AuNPs. The latter interaction occurs from carbonyl group and nitrogen atom within the lactam ring as demonstrated in PVP-based (co)polymers by combination of Xray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and Raman spectroscopy. [30] The effect of P(VCL-stat-VP)20k composition at a given polymer concentration is then TEM images for Au@PVCL, Au@P(VCL75-stat-VP25), Au@P(VCL50-stat-VP50) and Au@P(VCL10stat-VP90) and (C) Evolution of average size as a function of VP content (the line is only a guide for the eyes). (UV-vis spectra and TEM analyses were performed by H.H. (i) Colloidal stability

The effect of copolymer composition on the colloidal stabilization of particles solution subjected to an increase in pH or ionic strength was then evaluated after addition of NaOH (columns A2, B2, C2, D2) or NaCl solution (columns A3, B3, C3, D3) as shown in Figures II. 5 and II.7. In this experiment, a progressive change of color relates to the modification of plasmon band of the particles due to the fact that aggregation or sedimentation phenomena reflects a low colloidal stability. After addition of NaOH, at copolymer concentration of 10 -4 wt.%, the system is not stable and the nanoparticles aggregate to form larger aggregates cluster (column A2 in (ii) Effect of temperature on Au@P(VCL-stat-VP)20k properties

The effect of temperature on the resulted hybrid materials was then evaluated as shown in (iii) Catalytic efficiency of Au@P(VCL-stat-VP)20k

The catalytic performances of all Au@P(VCL-stat-VP)20k systems were further The observed rate constants (kobs) for all kinetics were extracted from linear relationship between ln (At/A0) versus time t assuming pseudo first-order kinetics for this reaction in the presence of an excess of NaBH4. Figures II.10B and II.10D display the fits of the experimental data obtained at different temperatures for Au@P(VCL75-stat-VP25) and Au@PVCL catalysts, respectively. At the beginning of reaction stage, there is an induction period which is related to a surface restructuring of the nanoparticles before the catalytic reaction starts. [32] The reaction can occur only between species adsorbed on the surface. The evolutions of pseudo-first order kinetic constant (kobs) as a function of temperature for Au@P(VCL75-stat-VP25) and Au@PVCL are given in Additional results obtained at 20 °C for different Au@P(VCL-stat-VP)20k systems are given in Figure II.12. At 20 °C, hybrid nanoparticles based on statistical copolymers present higher kobs values than those evaluated for Au@PVCL and Au@PVP. Moreover, an optimum kobs is measured when VP content equals to 50%. The observed trend of catalytic efficiency as a function of copolymer composition can be rationalized as a compromise between two opposite effects. On the one hand, higher VCL content increases the hydrophobic character of organic shell surrounding AuNPs and thus favors the diffusion of reactants towards the AuNPs surface.

On the other hand, the stronger adsorption of VCL compared to VP limits the catalytic efficiency of resulting nanohybrids.

II.4 Conclusions

The stabilization of AuNPs based on PVCL enables the access to hybrid thermosensitive materials with modular properties. [24,25] Though structurally close to PVP, studies on PVCL are much less prevalent. In order to compare the ability of these two families for the formation, stabilization and modulation of the properties of AuNPs, a series of VCL/VP statistical copolymers with controlled molecular weights and low dispersity, containing variable amounts of VP (ranging from 0 to 100%), was synthesized by RAFT/MADIX polymerization. The effect of the copolymer composition was evaluated both on the growth of AuNPs prepared in the presence of the polymers (in situ route) and on the properties (stabilization, optical and catalytic properties...) of preformed nanoparticles coated by these (co)polymers. With two additional methylene group per monomer unit in comparison with PVP, PVCL demonstrates strong differences concerning its ability to interact with and stabilize AuNPs. As demonstrated through this chapter, its increased hydrophobic character enables PVCL to act as a more effective stabilizing and growth control agent than PVP for the in situ synthesis of AuNPs. Moreover, whatever the method of preparation of nanohybrids used (in situ formation or coating of preformed AuNPs), statistical copolymerization of VCL and VP makes it possible to modulate to some extent the properties of polymer, and thus of the obtained hybrid materials. Hence, at a molar fraction of VP in copolymer less than 40%, it is possible to increase the transition temperature of the hybrid material and improve catalytic property compared to counterparts comprising PVP and PVCL homopolymers. In addition, incorporation of higher fraction of VCL units in P(VCL-stat-VP)20k promotes an increased colloidal stability of AuNPs.

The results obtained on AuNPs in this chapter can be used to extend the scope of PVCLbased copolymers for the synthesis of functional colloidal materials based on the different inorganic supports as described for PVP [30] or for the formation of thermosensitive hybrid nanogels [33,34].

II.5 References

[1] K.K. Harish, V.

III.1 Introduction

Synthetic materials capable of responding in a controllable and predictable fashion to small changes in their environment (temperature, pH, mechanical stress…) have aroused great interest in the last decades. This response induces changes in the properties of these materials such as dimensions, internal structure or aggregation state. [1] In that context, thermosensitive systems, obtained by dissolving a polymer in aqueous solution, have been extensively studied.

They present a characteristic transition temperature called cloud point temperature (Tc) at which the interactions between the polymer chains and the aqueous media dramatically change. This results in the collapse or expansion of polymer chains. If, in the phase diagram, a change from a two-phase to a single-phase system is observed when the temperature is increased, an upper critical solution temperature (UCST) is defined. In the opposite case, a lower critical solution temperature can be defined (LCST). Among all polymers presenting LCST, like poly(Nvinylcaprolactam) (PVCL), [2,3] poly(oligo(ethylene glycol) methacrylate), [4] etc…, poly(Nisopropylacrylamide) (PNIPAM) is by far the most commonly described. [5,6] Their thermoresponsive properties are used in stimuli responsive drug nanocarriers and functional surfaces with tunable hydrophobicity. [2,[7][8][9] Interestingly, the choice of the macromolecular parameters of a chosen polymer (composition, molar mass, architecture…) greatly influences the properties of obtained materials. The Tc remains almost constant whatever the molar mass in the case of PNIPAM, [2] but changes along with a strong, concentration-dependent polymer-solvent interaction.

However, this temperature can be precisely controlled by the adjustment of molecular weight (Mn) in the case of PVCL with a value tending to increase with the decrease of copolymer chain length. Polymer architecture (linear, branched, hyperbranched, grafted…) also influences thermoresponsiveness of these polymers. For example, four-arm PNIPAM stars collapse to form denser globules than the ones observed for linear PNIPAM [10] and PNIPAM-based branched thermoresponsive gels do not show the same kinetics of hydration and rheological properties when compared to their linear counterparts. [11,12] Incorporation of hydrophilic or hydrophobic comonomers within random or block copolymers enables to finely tune LCST values: [13] random copolymerization with a 82/18 molar ratio of NIPAM with hydrophilic acrylamide monomer increases Tc value from 32 to 45 °C. [14] Similarly, random copolymerization of VCL with hydrophilic comonomers (i.e. Nvinyl formamide, N-methyl-N-vinylacetamide or vinylpyrrolidone (VP)) induces a significant increase of Tc. [15,16] Thus copolymerization appears to be an effective means of modulating 112 Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Tc, even if, in most case, this variation does not depend linearly on the comonomer ratio. [15] Moreover, this incorporation can lead to a rapid loss of heat-sensitive properties. [15,16] On the contrary, an incorporation of a hydrophobic monomer tends to decrease the observed transition temperature. Thus, statistical copolymerization of NIPAM with hydrophobic acrolein using a 80/20 molar ratio induced a decrease of Tc value down to 26 °C, [14] a similar tendency was observed in cases of block copolymers. In addition, below Tc, their specific microstructure confers an amphiphilic character to this block structure, this results in the formation of selfassemblies such as micellar structures or polymersomes. [13] Above Tc, the dehydration of the thermoresponsive block induces aggregation of the preformed nanoobjects.

In this chapter, copolymers of NIPAM and hydrophobic n-butyl acrylate (BA) were considered. Whereas this family of copolymers can act as stabilizers for nanoparticles [13] or emulsion systems, [17] few studies have described their properties in aqueous solution yet. [13,[17][18][19][20] For instance, P(BA-stat-NIPAM) statistical copolymers have been used to form hydrogels for which a decrease of Tc from 34.3 to 29.5 °C was observed when BA content increased up to 20 mol.%. [21] The specific structure of PBA-b-PNIPAM block copolymer enabled the formation of stable nanospheres both below and above Tc [13,19] with a significant increase of diameter above Tc. [13] Here, we aimed at further studying the properties of this family of copolymers at different temperatures and concentrations in relation with their composition and microstructure. For this, polymers with statistical, diblock and triblock microstructures were synthesized by reversible addition-fragmentation chain transfer (RAFT)/macromolecular design by interchange of xanthates (MADIX) copolymerization of NIPAM and BA. [13,17] The ability of different copolymer structures to associate as colloids in dilute solution and to form gels at higher concentration, and the temperature dependence of these properties were studied with turbidimetry measurements, differential scanning calorimetry, electronic microscopy, rheology and scattering experiments.

III.2 Synthesis and characterization of copolymers

In order to study the influence of copolymer composition and architecture on the thermoresponsive properties, three families of copolymers were investigated: P(BA-stat-NIPAM) statistical copolymers, PBA-b-PNIPAM diblock copolymers and PNIPAM-b-PBA-b-PNIPAM triblock copolymers. For each family of them, a similar Mn value of 10000 gmol -1 (abbreviated as 10k) was selected. (Ctr,X1 = 2.7 [22] and 3.3 [23] for BA and NIPAM in ethanol, respectively). The Mn of PNIPAM synthesized in the presence of X1 or X2 is nearly twice as high as the theoretical Mn value when SEC analysis was performed in DMF. We attribute these differences in Mn to differences in hydrodynamic volumes between PMMA and PNIPAM in DMF/LiBr eluent, as the Ctr,X1 value of 3.3 for NIPAM rules out the possibility for the xanthate to be partially reacted at the end of the polymerization. As reported in Table III Thermal properties of block copolymers. DSC analysis was performed for all homopolymers, statistical and block copolymers. As expected glass transition temperature of statistical polymer decreases from 111.9 to 100.4 °C when BA content increases from 5 to 20 wt.% within the copolymer (see Table III.1). Whereas block copolymers with 50/50 weight composition show two glass transitions temperatures (around -50 and 100 °C), 2k/8k copolymers present only one around 100 °C. In the latter case, the lower weight fraction of BA within the copolymer prevents the possibility to undergo the transition corresponding to this block. Interestingly, the observed Tg values for triblock copolymers are found at lower temperature than the one observed for corresponding diblock or statistical copolymers, this suggests there is a different phase separation of two blocks in the solid state.

III.3 Determination of cloud point temperatures of copolymer solutions

In order to evaluate the influence of composition and microstructure on Tc values, the behavior of polymer solutions was studied as a function of temperature at concentration ranging from 0.1 to 20 wt.%. Among synthesized (co)polymers, only those with a minimum PNIPAM Whatever the technique used, a sharp and reversible phase transition was observed. In addition, when comparing the behavior of polymer solutions upon cooling or heating, a hysteresis phenomenon whose amplitude depending on the chosen heating/cooling rate is observed. This phenomenon is related to the difficulty of swelling compact aggregates formed at higher temperatures due to intra-chain entanglement. [25] In reported for a constant amount of PNIPAM decrease significantly when the amount of PNIPAM decreases. Hence, in the case of statistical copolymers, ΔH values equal to 31.58, 13.33 and 2.25 J•g -1 of PNIPAM are reported for a PBA content of 5, 10 and 20 wt.% respectively. Similar trends were observed for diblock and triblock copolymers but, as expected, in a lesser extent.

Indeed, for these copolymers, disruption of hydrogen network is less expected due to the presence of large PNIPAM moieties. In addition to this composition effect, the effect of the microstructure is highly pronounced. Hence, for a given composition (i.e. 80 wt.% of PNIPAM), the Tc measured for a statistical copolymer is well below the one measured for triblock and diblock structures (9.62, 25.13 and 27.60 °C, respectively). In the case of a statistical copolymer, its specific microstructure seems to strongly disadvantage the hydration of the copolymer. It also does not enable to study copolymers containing BA fractions greater than 20 wt.%. Lastly, the slightly lower values of Tc for triblock structures compared to diblock ones might be related to a similar phenomenon: indeed, for a given composition, triblock structures present one supplementary transition between PBA and PNIPAM blocks.

III.4 Properties of block copolymer in dilute aqueous solution

In addition to effect on cloud point temperature, the microstructure also strongly impacts the solubility of the different studied copolymers. Hence copolymers with a statistical structure present a low solubility in aqueous solutions (limited to 1 wt.%), whereas diblock and triblock copolymers thanks to their specific amphiphilic structure enable to obtain clear solution for weight fraction up to 20 wt.%. This observation might be related to the formation of nanometric colloidal suspensions and will be studied in the following section.

III.4.1 Phase behavior in water at low temperature (T < Tc)

As evidenced by DLS measurements, block copolymers behave as isolated chains at concentration of 0.1 wt.%. When they are transferred from organic solvent into aqueous solutions, a significant increase of their hydrodynamic radii are observed by DLS whereas only a slight change is seen for homopolymers (Table III.3), suggesting that they have the ability to self-assemble. Additionally, Transmission Electronic Microscopy (TEM) and Small Angle Neutron Scattering (SANS) measurements were carried out to analyze the size and larger micelle size. The average aggregation number (Nagg) of these micelles can be assessed from the following formula by considering a dense and solvent excluded core:

N agg = 4πρ core R core 3 N A /(3M core ) (1)
Where Rcore is radius of the core, Mcore is the mean average molar mass of core block (here Moreover, for diblock copolymers, radii are equal to 52 ± 7 nm and 53 ± 8 nm for PBA2kb-PNIPAM8k and PBA5k-b-PNIPAM5k respectively. Thus, at temperature above Tc, these aggregates have similar size whatever the nature of microstructure (diblock or triblock). The formation of spherical aggregates also named mesoglobules has been previously described in the case of PNIPAM homopolymers [27,28] as well as of hydrophobically modified PNIPAM polymers and PNIPAM-based amphiphilic block copolymers. [13] These mesoglobules are stable in aqueous solution and they spontaneously transform into spherical micelles when the solution is cooled below Tc: formation of larger aggregates is prevented by the low probability of Brownian collisions in dilute solutions. [27] At temperature above Tc, polymer chains dehydrate and as a result intrachain contraction and interchain association occur, which gives rise to the formation of large aggregates with poorly hydrated property. Consecutively to the further ejection of water molecule to bulk water, very dense and rigid mesoglobules are formed.

Mcore = MPBA), core is 1.1 g•cm -3 ,
The probability of merging of different mesoglobules might be very low due to the very short contact time between two mesoglobules during a collision or due to partial vitrification taking place within the dense mesoglobules.

[29]

III.5 Formation and characterization of thermosensitive hydrogels

The behavior of polymer solutions for concentrations ranging from 0.1 to 20 wt.% was then studied. For this range of concentration, DSC measurements do not show significant changes in the measured transition temperatures Tc whatever the considered structures (diblock or triblock). Related enthalpy variation normalized with respect to PNIPAM content shows a strong decrease when the concentration increases. As such a decrease is not observed in dilute conditions, it tends to demonstrate a clear difference between the different polymers concerning the polymer/polymer and polymer/solvent interactions in gel solution. Interestingly, the concentration effect is proved to have a strong impact on the rheological properties of the studied solutions. intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state). intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state). to be much higher than the entanglement concentration which can be evaluated around 3 wt.% in the case of PNIPAM10k. [31] Interestingly the synaeresis effect inducing the formation of dehydrated gel is strongly related to the chemical structure of the (co)polymer. Whereas homopolymer and triblock copolymers present a pronounced synaeresis effect after only few minutes, diblock structure is less prone to demonstrate such an effect. Results from literature also demonstrate that gels obtained from branched or statistical structure favor the formation of gels without pronounced synaeresis effect. [12,15] In addition to the structure effect, the effect of composition was also studied. As shown in (heating rate of 1 °Cmin -1 used for rheology experiment). Moreover, a sufficient level of dehydration of the polymer is required in order to form the gels. Concerning the mechanical properties of obtained gels, the stiffness of the gel obtained from triblock structure is much higher than the one issued from diblock structure (G' equal to 3000 and 100 Pa respectively).

These values are found significantly higher than the ones observed for homopolymer Before the transition, typically G" > G', while after the transition, G' becomes (slightly) higher than G" for both copolymers. In more details, the measurement of G' and G" with a frequency sweep for sol and gel phases has been performed to determine the viscoelastic nature of these phases (see Figure III.38). These measurements confirm the gel status for both triblock and diblock gels at 31 and 35 °C, G' and G" being nearly independent of the frequency from 10 to 0.1 Hz. Conversely, at 20 °C, when both copolymers preparations are liquid, G' and G" display a typical behavior of viscoelastic fluids that follow a Maxwell model: at low frequencies G' is proportional to (f) 2 and G" is proportional to f. G' and G" curves cross at a quite high frequency around 10 Hz, which gives an indication of the relaxation time of both polymer solutions, t  0.018 s (triblock) and 0.015 s (diblock). A small hysteresis effect is observed for diblock copolymer when cooling the solution to room temperature. For the triblock copolymer, a more pronounced hysteresis effect was observed that could be related to the higher viscosity and relaxation time than with the diblock copolymer that could affect the mobility of polymer The properties of these hydrogels are likely to be strongly related to their internal structures.

Thus, to gain insight into the network structure of hydrogels, freeze-dried samples were analyzed with scanning electron microscopy at cryogenic temperature (see

Figure III.40).
Thus, the study of concentrated polymer solutions makes it possible to highlight the crucial effect of microstructure on macroscopic properties. For the same composition, the triblock structure leads to denser networks more likely to be the seat of important synaeresis and presents slower rehydration kinetic. The freeze-dried hydrogels show honeycomb-like microstructures with dense cell walls. Nevertheless, the cell/pore average size differs strongly, decreasing from diblock to triblock structures. Therefore, a clear relationship between molecular architecture and microstructure is evidenced: for a similar chemical composition, triblock structure promotes denser network structure with smaller pore size. A good correlation is observed between the increase of G' modulus and the apparent density of the gels. This difference of microstructure could also explain the differences observed on synaeresis effect between diblock and triblock structures, since less dense networks might accommodate easily a large volume of solvent.

III.6 Thermoresponsiveness of copolymers at different conditions

Numerous studies in the past have already compared the properties of polymers with different microstructures but similar compositions in solution. For instance, solutions of statistical and block copolymers present different rheological properties. [32,33] In the particular case of thermoresponsive polymers, branched and hyperbranched structures have been demonstrated to strongly affect the properties of PNIPAM-based polymers either in dilute conditions or in gel phase, [11,12] and block copolymers with statistical structure present cloud point temperature more sensitive to their composition than block counterparts. [15,34] Through this study we compared in a systematic way the effect of composition and microstructure (statistical, diblock and triblock) on properties in solution of amphiphilic thermoresponsive copolymers at different concentrations and temperatures. The transition temperature of these copolymers in solution depends, as expected, on their composition: an increase of the fraction of hydrophobic part leads to a decrease of transition temperature. This temperature also depends on the microstructure at a given composition: in comparison with block structures, the statistical structure is detrimental, as expected, to the good hydration of hydrophilic monomers due to their microenvironment, thereby leading to a significant decrease in transition temperatures.

Below the transition temperature, block copolymers have an amphiphilic character, which leads spontaneously to the formation of colloidal structures above a critical aggregation concentration (cac) as illustrated in Scheme III.1. Their existence promotes the dispersibility of these copolymers in aqueous solution even at high concentration. The structure of objects formed depends in particular on the composition of block copolymer and on the preparation method used. [35] Moreover the rate of exchange of polymer chains within these objects primarily depends on the interfacial tension between hydrophobic block and water as well as the length of hydrophobic block and (co)polymer architecture. Due to a too large interfacial tension, exchanges are absent for large hydrophobic blocks as observed in the case of BA-based copolymers which lead to kinetically frozen aggregates. [36] Hence, different groups have reported that PBA-based amphiphilic block copolymers do not reorganize, or only very slowly, in spite of liquid like behavior of their hydrophobic blocks. [37][38][39] To induce faster exchange of polymer chains within these aggregates, copolymerization of hydrophilic units like acrylic acid in the PBA block can be used, it reduces the interfacial tension between the moderately hydrophobic block and the hydrophilic block and water. [40] Moreover, in the case of PBA-b-PNIPAM copolymers, the incorporation of hydrophilic units of dimethyl acrylamide within PBA block showed that decreasing degree of hysteresis is associated with the thermal transition.

[20] All these results from literature suggests that, below Tc, PBA-b-PNIPAM diblock and PNIPAM-b-PBA-b-PNIPAM triblock structures act as frozen micelles above a critical aggregation concentration. Also as demonstrated by DLS and SANS measurements and as discussed above in Section III.4, compared to diblock copolymers, triblock counterparts lead to smaller and less dense frozen micellar structures with significantly lower aggregation number.

Above the transition temperature and at low concentrations, for a chosen polymer structure, the formation of colloidal aggregates (i.e. mesoglobules) is observed. These nanoobjects are issued from the dehydration of PNIPAM corona of previously described micelles. The frozen PBA core prevents further reorganization of the polymer within and between the aggregates.

Thus, by decreasing temperature below Tc, a fast hydration process of PNIPAM corona is possible. This mechanism enables a fast and reversible formation of so-called mesoglobules from diblock and triblock structures. These aggregates have similar size whatever the nature of microstructure (diblock or triblock). At higher concentrations the formation of gels is observed (see Scheme III.1). Their formation might be related to the interconnection of dehydrated micelles in the whole solution when a sufficient concentration of nanoobjects is reached.

142 Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Diblock structures, compared to triblock structures, allows the formation of gels that are softer than triblock gels but that do not demix with time (no synaeresis). This might be ascribed to the ability of diblock structures to favor the formation of more efficiently interconnected network of dehydrated frozen micelles that have less tendency to aggregate as demonstrated in the case of dilute solutions. Triblock structures compared to their diblock counterparts form stiffer and more viscous gels, with high synaeresis and slower rehydration kinetics. These properties can be related to the nature of hydrogen-bonded network, which is denser and therefore with smaller pores due to the reception of a smaller quantity of solvent.

Scheme III.1 Schematic illustration of behaviour of diblock and triblock copolymers in solution as a function of concentration and temperature. For statistical copolymers, no micelle or gel were observed, only a transition towards a turbid solution above Tc.

III.7 Conclusions

The microstructural engineering of amphiphilic thermoresponsive copolymers of n-butyl acrylate and N-isopropylacrylamide allows significant modulations of self-assembly, morphological and mechanical properties of these materials in aqueous media. With similar composition, the hydrophobic acrylate monomer in block copolymers contributes to a decrease of cloud point temperatures compared to pure PNIPAM and to a much lesser extent compared to statistical structures, and enhances their solubility in aqueous solutions via self-assembly. In addition, below the cloud point temperature, block structures of appropriate composition lead to the formation of colloidal aggregates. Above this temperature, the formation of colloidal aggregates is observed at low concentration, and gels are formed at higher concentration. For a given composition, scattering experiments demonstrate that diblock structures lead to smaller colloids and mesoglobules than their triblock counterparts. Moreover, diblock copolymers lead to larger and denser structures compared to triblock analogues and allow the formation of gels that do not demix with time (no synaeresis) but they are softer than triblock gels. While results in the literature have already demonstrated the important effect of architecture [11,12] or microstructure [32,33] on the properties of polymer solutions, the effect of microstructure on properties of amphiphilic polymer assemblies has been more rarely reported. [40] Our study based on a thermosensitive polymer family also shows the striking effect of microstructure related to temperature on solution-generated organizations. Further studies will concern amphiphilic gradient copolymers [41]

IV.1 Introduction

Stimuli-responsive (co)polymers [1][2][3] have attracted a great interest in recent years due to their ability to respond macroscopically, rapidly and reversibly to changes in their local environment, opening the way to multiple promising applications in areas from material science to biology.

External stimuli can act as triggers that can be applied as chemical or physical or biological signals. Physical signals such as temperature, electric or magnetic fields, light and pressure modify the energies of chain dynamics and alter molecular interactions near critical points.

Chemical signals, such as pH, [4] ionic species or biochemicals modify the conformations of polymer chains and the interactions between (co)polymer chains and solvents. Biochemical stimuli such as enzymes, [5,6] antigens and biochemical agents contribute to promising biomedical applications such as controlled drug release.

One of the most significant class of stimuli-responsive (co)polymers are thermo-sensitive (co)polymers, [7][8][9] which are widely investigated due to the easy control of temperature change and the ease of their applications. This family of (co)polymers exhibits a soluble-to-insoluble phase transition at a lower critical temperature (LCST) or an insoluble-to-soluble phase transition at upper critical solution temperature (UCST). Various LCST-type thermoresponsive Among them, the most well-known and extensively studied thermoresponsive homopolymers are PNIPAM which exhibits a reversible phase transition from a hydrophilic coil state to a hydrophobic globule state as temperature increases above LCST. [12] The Nalkyl group in N-alkyl-substituted polyacrylamides is an important parameter to determine the thermo-response and phase behavior of polymer solution. For example, poly(N,N- To prepare multi-responsive (co)polymers, one strategy is to develop multi-responsive homopolymers. However, very rare examples have been reported certainly due to the laborious synthesis of the monomers containing at least two differently functional moieties. For example, Huang et al. have described the synthesis of a homopolymer by polymerization of a dual responsive monomer containing both isopropylacrylamide and N,N-diethylaminoethyl moieties in the side chain. [19] The LCST of this homopolymer can be tuned by changing pH value of aqueous solution, and it increases with the degree of protonation of the tertiary amine groups.

Another strategy widely documented is to combine several stimuli-responsive moieties within random, block, gradient or graft copolymers containing two or more than two stimuliresponsive segments or blocks. Diblock copolymers consisting of one thermoresponsive block (PNIPAM) and one pH-responsive block bearing tertiary amine moieties (i.e. poly(2dimethylamino) ethyl acrylate) (PDMAEA), [20] PDEAEMA… [21,22]) have been reported

with tunable self-assemblies in aqueous media upon variation of solution pH and temperature.

In this chapter, we aimed at studying a family of block copolymers comprising of a thermo-

IV.2 Synthesis and characterization of homo-and copolymers

DEAEAM monomer was synthesized according to a previously described synthetic pathway. [24] Well-defined thermo-and pH-responsive diblock copolymers comprising of PNIPAM and PDEAEAM blocks were further successfully synthesized by reversible additionfragmentation chain transfer radical (RAFT) polymerization using 2,2'-azobisisobutyronitrile (AIBN) as free-radical initiator and 4-cyano-4-[(dodecylsulfanylthiocarbony) sulfanyl] pentanoic acid (CDTPA) as RAFT agent. This chain transfer agent (CTA) was chosen due to its known reactivity for both monomers leading to a well control of polymerization. [23,24] It Mn,NMR

is
(g• mol -1 )
Mn,SEC

IV.3 Thermoresponsive behavior of homopolymer solutions

To understand the thermoresponsive properties (phase transition temperature and selforganization behavior) of PN-b-PD under different conditions, the thermosensitive behaviors of PN and PD homopolymer solutions were investigated firstly.

IV.3.1 PN homopolymer

PNIPAM is by far the most commonly described thermoresponsive homopolymer.

Incorporation of hydrophilic or hydrophobic comonomers enables to finely tune cloud point temperature (Tc) as stated in Chapter I. [26,27] For example, when NIPAM is statistically copolymerized with hydrophilic monomers such as acrylamide, Tc increases up to about 45 °C when the polymer chain comprises 18 mol% acrylamide, whereas Tc decreases to around 26 °C when 20 mol% hydrophobic acrolein is incorporated into the polymer chain. [26] To a lesser degree, similar effects are observed in the cases of (co)polymers with various architectures (block, branched…). [27][28][29] Interestingly terminal groups also have a strong influence: hydrophobic terminal groups decrease Tc, whereas hydrophilic ones tend to have a reverse effect. [30] In the case of ionizable end groups, their hydrophilicity varies with the proportion of ionized form related to pH range. The more the ionized form is present and the more the hydrophilicity of the end of chain is marked, Tc of (co)polymer will be increased.

Here, synthesized PNxk homopolymer chains contain, at pH 4, one hydrophilic carboxylic acid function on one side and a hydrophobic -C12H25 group on the other side (Scheme IV.6).

These two groups play a key role in thermoresponsive property of PNxk homopolymers in aqueous solution. Meanwhile, one point should be noted that increasing concentration tends to lower Tc. The pH-dependence of Tc can be attributed to the degree of ionization of -COOH end group. Compared to -COOH group, -COO -has a better solvation and helps to improve PN5k solubility in water. With rising pH, the amount of -COO -groups in solution becomes larger and results in an increase of Tc value. Such trend was previously reported in the cases of linear and star-type PN homopolymers terminated with -COOH or ionizable groups (pKaCOOH = 4.5 ± 0.1).

[ 24,30,32] In addition, the absence of transition observed at high pH value is ascribed to the formation of micellar system which hinders phase separation. For instance, PN polymers synthesized by RAFT polymerization using S-1-dodecyl-S-(α,α'-dimethyl-α,α'-acetic acid) trithiocarbonate as a chain transfer agent form micelles in aqueous solution with a core of hydrophobic terminal dodecyl groups and a corona of PN chains with carboxylic groups at the periphery, the ionization of which prevents phase separation of PN at temperature above Tc.

Instead, a sphere-to-rod transition of micelles was observed by SANS. [30] In order to confirm the formation of micellar system and the critical role of end group, DLS measurements were Moreover, it is noted that the carboxylic end group is in its deionized form at pH below pKaCOOH. As peaks relative to PD are less modified than the ones corresponding to PN, this indicates that PD polymer chains present a higher mobility in aqueous solution. This might be ascribed to the formation of aggregates with core-shell structure, where PN is in the core and PD is mainly in the shell, causing PD has lower T1 and less pronounced modification of integration than PN. DLS experiments enable to evaluate an average hydrodynamic diameter of 27.0 ± 8.8 nm.

Therefore, as observed in the case of PN5k, PN5k-b-PD5k in aqueous solution is prone to selfassemble into micellar structure with a core of -C12H25 group and a corona of PN and PD blocks.

The presence of carboxylate function enables to limit the aggregation to the formation of quite small spherical colloidal system. (iii) Characterization of obtained aggregates below and above Tc,1 and Tc,2

The colloidal structure obtained from aqueous solution of PN5k-b-PD5k were studied by TEM and DLS at 25 (below Tc,1), 30 (between Tc,1 and Tc,2) and 60 °C (above Tc,2). All results are summarized in Table IV.4. To avoid aggregation phenomenon at 1 wt.%, solution with a dilute concentration equal to 0.1 wt.% was studied. It is noteworthy that aggregates size measured above Tc is demonstrated in previous section that it highly depends on the method of Further experiments using multi-angle dynamic light scattering and static light scattering are still in progress to determine the hydrodynamic radii (Rh), aggregation numbers (Nagg) and average molecular weights of the assemblies formed above and below Tc whatever the pH.

These data could provide complementary information on the morphology of the aggregates formed at different conditions, which could gain a deeper understanding of the observed differences induced by the modification of composition.

IV.5 Conclusions

Thanks to the RAFT polymerization process a series PN-b-PD copolymers and corresponding homopolymers have been successfully synthesized with controlled molecular weight and composition. The behavior of these (co)polymers in aqueous solutions was studied as a function of temperature and pH. We demonstrate in the case of PN homopolymer the key role of functional end-groups on its aggregation properties in water. Aggregation properties (size, phase transition temperature) of block copolymer depends strongly on pH value, composition and the history of formation. At pH 4, solely PN block is thermoresponsive.

Solutions of

V.1 Introduction

Carbon dioxide (CO2) has emerged as a new and innovative trigger for stimuli-responsive materials due to its abundant, inexpensive, nontoxic and environmentally benign properties.

CO2-switchable polymers are a class of stimuli-responsive polymers in which CO2 is used to induce modification of polymer properties (such as solubility, dimension, chain conformation and morphology…).

The immediate origins of these changes result from a neutral to charged state (or vice versa) of functional groups within polymer structure (i.e. amidines, tertiary amines). Indeed, as depicted in Scheme V.1, the dissolution of CO2 in water acidifies the solution due to the dissociation of both carbonic acid and hydrated dissolved CO2.

Scheme V.1 Equilibria involved in the dissolution of CO2 in water

Further reversible reactions of CO2 with various organic compounds are the basis for CO2triggered switchable substances. Neutral (uncharged) amines, amidines and guanidines can be converted to bicarbonate salts upon exposure to CO2 in the presence of water (in eq. ( 1), B represents organic base). Amines, amidines and guanidines having N-H bonds can be converted to carbamate salts upon exposure to CO2 illustrated in eq. ( 2) in the case of a secondary amine.

By applying air or any nonacidic gas (such as N2 or Argon) along with heating, CO2 can be removed and active stabilizer is switched to a neutral form. The most important feature of these systems is that, during these transitions, CO2 will not be accumulated in a system upon repeated cycles.

The basicity is required for facile switching depends greatly on the temperature and on the concentration at which the species can be switched. Ideally, the protonation degree is very low 190 Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer when the system is under air, and in the presence of CO2 it should be as high as possible to maximize the property change in polymer solution (Scheme V.2). Thus, the addition and removal of CO2 should take the mixture back and forth across the system midpoint, which is defined as pH at which half of the switchable groups are protonated. Under air, the pH should be significantly higher than system midpoint, while upon exposure to CO2, pH should be significantly lower than system midpoint. If the switchable species is entirely dissolved in the aqueous phase under air and under CO2, the system midpoint is equal to pKa value.

Scheme V.2

The principle of CO2-switchable system in water. [1] Among neutral switchable species, amines have appropriate basicity in water to be CO2- In this chapter, we aim at studying the CO2-induced thermoresponsiveness of homopolymer, poly(N-,N-diethylamino ethyl acrylamide) (PDEAEAM), which bears thermoand pH-/CO2-responsive groups (acrylamide and tertiary amine group within one chain) and is one of multi-stimuli responsive homopolymers. Its corresponding cloud point temperature (Tc) can be tuned ranging from 50.2 to 33.1 o C with a pH change from 8.5 to 11.0. Moreover, its LCST behavior disappears upon CO2 treatment and can be reversibly recovered by bubbling inert gas. [2] However, literature involving PDEAEAM-based copolymers is relatively scarce.

generate bicarbonate salts when a small quantity of CO2 is added, [7,16] while those bearing primary amines (such as poly(allylamine)) generally form into carbamates. [17] In order to clarify the CO2/N2 switchability of PD, we first studied pH changes of PD5k solution when CO2 and N2 were introduced alternatively. Protonation degree is calculated by the following eq. ( 3):

% protonation = 1 1+10 pH-pKa (3)
As depicted in Figure V.1A, before bubbling CO2, system pH is 9.28 while corresponding protonation degree is 0.92%, thus PD5k is regarded in deprotonated state. With introduction of CO2 for 2.5 min, pH decreases sharply to 5.5, while a dramatic increase of protonation degree changes from 0.92 to 98.3%. After, both pH and protonation degree do not alter along with CO2 concentration in system. As N2 is alternatively bubbled, pH rises to 8 whereas protonation degree falls down to 15% after 5 min N2 bubbling, which is followed by a slow increasing and decreasing tendency for changes of pH and protonation degree along with N2 quantity, respectively. After 20 min bubbling N2, pH returns to 8.53 and protonation degree comes to 5%. The reversibility of pH and protonation degree upon bubbling CO2/N2 were traced (see and -CH2CH2N(CH2CH3)2, respectively. After 10 min of bubbling CO2 (to make sure all PD units are protonated), these signals shift to 3.56, 3.27 and 1.32 ppm, respectively, and changes in system pH (from 9.9 to 6.1) and protonation degree (from 0.2 to 94%, calculated by eq. ( 3)) are accompanied with this process. Meanwhile signal at 160 ppm in 13 C NMR spectrum reveals the formation of ammonium bicarbonate (see Figure V.2C). After 30 min N2 treatment, proton 194 Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer peaks do not return to their original positions but shift to 3.39, 2.80 and 1.14 ppm, respectively.

Figures V.1B
Additionally, pH of PD5k goes up to 8.8, these results suggest that there is still a small quantity of PD5k in protonated state (protonation degree is around 3%), more time of N2 bubbling or heating PD5k solution is needed for the complete recovery. Simultaneous coexistence of acrylamide and tertiary amine groups endows PD homopolymers with thermo-and CO2-responsive properties. As shown in the previous chapter, their thermo-sensitivity is influenced by pH adjustment due to the protonation/deprotonation of tertiary amine groups. Here, CO2 addition/removal can also modulate thermoresponsive properties of PD. Additionally, after removal of CO2 by exposure to N2, residual bicarbonate salts are prone to slightly modify the thermoresponsive behavior of PD in aqueous solutions.

To study the effect of CO2 on thermoresponsiveness of PD5k, turbidimetry measurements of PD5k as a function of temperature upon alternative bubbling CO2/N2 were performed (Figure

V.3A).

Before exposure to CO2, PD5k displays a LCST behavior with a measured Tc at 31.5 o C.

After treatment with CO2, tertiary amine groups are protonated, which makes PD5k hydrophilic.

The transmittance value remains constant around 100% from 20 o C to 80 o C, suggesting that PD5k loses its thermoresponsiveness in the studied temperature range. Upon exposure to N2, the LCST behavior of PD5k is recovered with a higher Tc (64.9 o C). This phenomenon can be ascribed to the presence of residual CO2 species in interactions with tertiary amine, being in good agreement with Zhang's work. In CO2-rich environment, due to the protonation of PD5k chains, Tc is shifted to higher temperature. As temperature is raised above 60 o C (apparent Tc), a slight increase of size is observed. This unexpected trend can be ascribed to a partial decarbonation phenomenon. Indeed, heating polymer solution at higher temperature for a long period of time is also a useful method to remove CO2. When 30 min N2 was bubbled to drive CO2 out of the system, the responsiveness of PD5k is recovered with a higher Tc at 52 o C, which is identical to the value (53 o C) obtained from turbidimetry measurements.

V.3 Thermo-and CO2-responsiveness of PN5k-b-PD5k block copolymer

Block copolymers generally combine all properties of each block within structure. Thus, synthesized PN5k-b-PD5k block copolymers are expected to have both thermo-and CO2responsive properties. In all cases the addition of CO2 deeply modifies the value of Tc of studied copolymers.

After bubbling N2, none of the systems returns to initial state due probably to the presence of residual ammonium bicarbonate. Nevertheless, the magnitude of thermoresponsiveness shift relates to the length of PD chain. Due to the presence of longer PD block, the effect seems to be more pronounced in the case of PN2k-b-PD8k block copolymer than that in PN8k-b-PD2k.

V.4.2 Effect of copolymer composition on self-assembly behavior Obtained results are in good agreement with the ones observed in the case of PN5k-b-PD5k copolymers, leading to the similar conclusions. Further experiments (SAXS, Zeta potential…) are under way concerning the characterization of observed structures.

V.5 Reversibility of PN-b-PD upon alternate bubbling CO2/N2

As demonstrated above, exposure to CO2 enables to protonate tertiary amine groups in PD Lastly, we investigated CO2-responsiveness of PDEAEAM upon CO2 treatment/removal.

The effect of addition of CO2 on the behavior of PNIPAM-b-PDEAEAM block copolymer is studied and illustrated how colloidal properties (phase transition temperature and colloid formation) of this copolymer solution can be tuned by using different stimuli: temperature and CO2. Additionally, all these block copolymers of PNIPAM-b-PDEAEAM exhibit a good reversibility with at least 7 cycles upon alternate bubbling CO2/N2.

Experimental Section

aqueous solution of sodium hydroxide (NaOH, 1 molL -1 ) under vigorous stirring. The solution turned immediately dark red, indicating the formation of AuNPs (final concentration equal to 5×10 -4 mol•L -1 ). These colloidal solutions were stable but rapidly aggregated when salt was added. Then, a series of stock aqueous solutions of copolymer solutions at 2×10 -3 , 2×10 -2 , 0.1, 0.2 wt.% and a stock solution of preformed AuNPs at 5×10 -4 mol•L -1 were prepared separately.

Experiments were performed using a 96-well plate (Costar 96) with a well final volume equal Diblock copolymers of PBA-b-PNIPAM were synthesized as previously described (Scheme ES.3). [2] A typical procedure for synthesizing block copolymers of BA and NIPAM was as follows: 51 mg AIBN, 0.521 g xanthate X1, 4.994 g BA and 3.39 g ethanol were placed into a two-neck round-bottomed flask equipped with a magnetic stirrer and a reflux condenser.

The solution was then degassed for 15 min by bubbling argon. It was then heated at 75 °C for three hours, keeping a slow stream of argon in the reactor. After a given time, the mixture The obtained PBA macro-chain transfer agent was mixed with appropriate amounts of AIBN, NIPAM and ethanol (Table ES.2). The solution was then degassed for 20 min by bubbling Ar. It was then heated at 62 °C for three hours, keeping a slow stream of Ar in the reactor. The reaction mixture was then cooled down to room temperature and the polymer was analyzed. NIPAM conversions (> 97%) were determined via 1 H NMR spectra, comparing the signal area of vinyl protons (δ ∼ 5.5-6.4 ppm, 3H/molecule for NIPAM) to signal area of isopropyl methylene (δ ∼ 3.9-4.2 ppm, 1H/molecule). The thermal properties of the (co)polymer (in bulk and in solution) were determined by using a Mettler Toledo DSC 1 STARe System Thermal Analysis calorimeter equipped with a Gas Controller GC200. Glass transition temperatures (Tg) of bulk (co)polymers were determined at a heating rate of 10 °C•min

ES.3.9 Transmission Electron Microscopy (TEM)

A drop of (co)polymer aqueous solution was placed on a formvar carbon-coated copper TEM grid (200 mesh, Ted Pella Inc.) and left to dry under air at the chosen temperature. For samples needing negative staining, these samples were prepared by depositing a 6 µL drop of (co)polymer solution preheated at a given temperature for 20 min, onto TEM grid and dried at the same temperature, followed by a negative stain with uranyl acetate (2 wt.%) aqueous solution for 2 min, the excess solution was removed with a filter paper, sample was dried again at the same temperature. TEM observation was performed on a HITACHI HU12 operating at 70 kV, The size distribution of the particles was determined by measuring at least 100 particles in each sample, WCIF ImageJ software was used to give average diameter ± standard deviation.

ES.3.10 Cryogenic Transmission Electron Microscopy (cryo-TEM)

In Chapter IV, cryo-TEM images were acquired on a JEOL 2010F TEM instrument [200 kV field-emission gun (FEG)] equipped with a Gatan UltraScan 4000 camera and cryogenic sample holder using lacey carbon film grids (300 mesh Cu, Agar Sc. S166-3H) The solutions were preheated at the chosen temperature, then a small droplet of each solution was placed on an ionized grid, and the excess solution was blotted with a piece of filter paper. The thusobtained thin film of solution spanning the grid was quickly plunged into liquid ethane (∼90 K) that was cooled by liquid nitrogen. The samples were then kept in liquid nitrogen before transfer range, a wavelength of 7Å with a distance of 1m to reach high q values and a wavelength of 17Å and 4.8 m to reach low q values required to observe large objects. The neutron wavelength distribution Δλ/λ was 0.11. The incident collimation was obtained from two circular holes, one close to the sample with a 7 mm diameter and the second one of either 16 mm diameter, 2.5 m apart from the sample diaphragm for the two highest q domains, or of 12 mm diameter, 5 m apart from the sample diaphragm for the smallest q range. The scattering vector range thus reached was 0.0025 < q (Å -1 ) < 0.35. Scattering intensities have also been normalized by the incoherent signal delivered by a 1 mm gap water sample in order to account for efficiency of detector cells. Absolute values of the scattering intensity, I(q) in cm -1 , were obtained from the direct determination of the number of neutrons in the incident beam and the detector cell solid angle. [5] No background was subtracted to the copolymer sample scattering, thus a flat incoherent signal is observed at high q values. The scattering curves of diluted copolymer x

x Ré sumé de thè se

Scheme I. 1

 1 Scheme I.1 Phase diagram of thermoresponsive (co)polymers with LCST behavior.

. 1 .

 1 Table I.1 Typical LCST-type homopolymers and their corresponding Tc values (Tc for LCSTtype homopolymers determined at a specific homopolymer concentration, molecular weight, and end group). N-alkyl substituted poly(meth)acrylamides PNIPAM Tc: 32 o C [1] PNIPMAM Tc: 43 o C [2] PEAM Tc: 32.2 o C [3] PEMAM Tc: 70 o C [4] PDEAM Tc: 30 o C [5-8] PNnPAM Tc: 22.56 o C [9] PMnPAM Tc: 29.3 o C [10] PCPAM Tc: 38 o C [8] N-ester substituted poly(meth)acrylamides PNAEAA Tc: 51.5 o C [11] PNASME Tc: 44 o C [12] PNAGME Tc: 36.5 o C [13] PNAGEE Tc: 20.5 o C [13] P(MA-L-Ala-OMe) Tc: 35 o C [14] Poly(N-dialkylamino ethyl (meth)acrylamide)s PDEAEAM Tc: 34.5 o C [15] PEPyAM Tc: 30 o C [16] N-alkyl substituted poly(meth)acrylates PMEMA Tc: 34 o C [17] PDMAEMA Tc: 32.2 o C[17]

  Abbreviations: PNIPAM: poly(N-isopropylacrylamide), PNIPMAM: poly(Nisopropylmethacrylamide), PEAM: poly(N-ethylacrylamide), PEMAM: poly(N,Nethylmethylacrylamide), PDEAM: poly(N,N-diethylacrylamide), PNnPAM: poly(N-npropylacrylamide), PMnPAM: poly(N-methyl-N-n-propylacrylamide), PCPAM: poly(Ncyclopropylacrylamide), PNAEAA: poly(N-acetoxylethyl acrylamide), PNASME: poly(Nacryloylsarcosine methyl ester), PNAGME: poly(N-acryloylglycine methyl ester), PNAGEE: poly(N-acryloylglycine ethyl ester), P(MA-L-Ala-OMe): poly(N-methacryloyl-L-alanine methyl ester), PDEAEAM: poly(N,N'-diethylamino ethyl acrylamide), PEPyAM: poly(Nethylpyrrolidine acrylamide), PMEMA: poly(2-(N-morpholino) ethyl methacrylate),

Figure I. 1 ,

 1 Figure I.1, Tc can be evaluated from this transmittance curve at different stages: onset temperature, temperature at which 90, 50 and 10% transmittance reach, inflection point. These different values are not significantly different for (co)polymers presenting a sharp transition, in the case of broad transition, as depicted in Figure I.1A, the deviationbetween the maximum (Tc,10% transmittance) and minimum (Tc,onset) Tc values obtained by using different evaluation methods can reach up to 11.9 °C. Therefore, the way to evaluate the transmittance curve to obtain Tc should be treated carefully.[41]

Figure I. 1

 1 Figure I.1 Transmittance as a function of temperature for PNIPAM solutions: (A) Different evaluation methods for determination of Tc and (B) Thermal hysteresis observed in heatingcooling cycles (heating rate: 0.2 o C•min -1 , wavelength: 488 nm, PNIPAM concentration in (A) and (B) were 0.02 and 0.1 wt.% respectively). Copyright 2017. Reproduced with permission from WILEY-VCH Verlag GmbH & Co. kGaA. Ref.[41]

Figure I. 2

 2 Figure I.2 Evolution of hydrodynamic diameter and normalized scattering intensity of PMEO2MA (or PDEGMA) as a function of temperature (Mn: 13660 g•mol -1 , concentration: 1 mg•mL -1 ). Copyright 2020. Reproduced with permission from the Royal Society of Chemistry.Ref.[45]

Figure I. 3

 3 Figure I.3 Thermograms of (A) poly(propylene oxide) (PPO) aqueous solution (Mn: 2000 g• mol -1 , concentration: 0.5 wt.%, heating rate: 0.2 o C•min -1 ) and (B) poly((Nisopropylacrylamine)-stat-(dopamine methacrylamide)) solution (Mn: 17900 g•mol -1 , heating rate: 5 o C•min -1 , dash-dot line was 4 wt.% PNIPAM with Mn of 35000 g•mol -1 ). Copyright 2015 and 2019, respectively. Reproduced with permission from the American Chemical Society.Ref.[48,49]

Figure I. 4 . [ 50 ]

 450 Figure I.4 1 H NMR spectra of poly(N-(2-hydroxypropyl) methacrylamide)53-b-poly(2-(2methoxyethoxy) ethyl methacrylate)53 (PHPMAm53-b-PDEGMA53) in D2O at different temperatures ([PHPMAm53-b-PDEGMA53] = 0.67 wt.%, Mn = 17100 g• mol -1 , DEGMA content is 50 mol%, Tc = 308 K). Copyright 2020. Reproduced with permission from the Elsevier Ltd.Ref.[50]

  Figure I.5B), the possible reason may relate to the fact that raising temperature weakens the hydrogen bonding network and improves mobility of water.[50]

Figure I. 6

 6 Figure I.6 (A) Temperature-dependence and (B) Time-dependence at 330 K of T2 of HDO of PHPMA53-b-PDEGMA78 in D2O. Copyright 2020. Reproduced with permission from the Elsevier Ltd. Ref.[50]

Figure I. 7

 7 Figure I.7 (A) IR spectra of PNIPAM in H2O and in D2O at 25 o C. (B) IR difference spectra obtained by subtraction IR spectra measured at 25 o C from those measured at 40 o C. (C) Plots of ΔΔAT-25(2970-2991) (C-H stretching mode) in D2O and in H2O as a function of temperature.Copyright 2000. Reproduced with permission from the American Chemical Society. Ref.[59]

For instance,

  Tc values of P(DEGA60-stat-DMAm40) and P(DEGA50-stat-DMAm50) do not change in concentration range from 6 to 20 mg•mL -1 . [23] PNASME170 solution maintains Tc around 44 o C as polymer concentration is over 0.5 wt.%, [12] Tc (36.5 o C)

Figure I. 8

 8 Figure I.8 Phase transition diagram of PNIPAM in (A) water-methanol (open cycles) and water-acetone (filled cycles) solutions, and in (B) water-ethanol (filled and open triangles representing LCST and UCST behaviors, respectively). Copyright 2002. Reproduced with permission from the Elsevier Science Ltd. Ref.[90]

( v )

 v Effect of end groupTo prepare well-defined (co)polymers, people usually synthesize thermoresponsive (co)polymers by using controlled radical polymerization, such as atom transfer radical polymerization (ATRP), reversible addition-fragmentation chaintransfer (RAFT) polymerization. As a result, the initiators, terminators (or chaintransfer agents) as the end groups are inevitably introduced into (co)polymers, the transition points of which in aqueous solution are therefore affected due to the different polarities, especially for those (co)polymers with low molecular weights.Many efforts have been devoted to exploring the effect of end groups on Tc of PNIPAM, such as hydrophilic (i.e. amino, hydroxyethyl, propargyl, chloroethyl terminated groups) and hydrophobic (i.e. alkyl substituted end groups: propyl, isobutyl hexyl, octyl, dodecyl and octadecyl) groups.[78,79,100,112] Dodecyl terminated PNIPAM has a lower Tc around 25 o C, whereas Tc in the case without hydrophobic terminal is much higher (38 o C). [79] Another typical example was reported by Stöver and coworkers shown in Figure I.9.

Figure I. 9

 9 Figure I.9 (A) Chemical structure of initiators providing terminal groups to PNIPAM and (B) cloud point as a function of molecular weight for PNIPAM terminated with end groups

( 4 .Scheme I. 4 Scheme I. 5

 445 Scheme I.4 Schematic illustration of thermoresponsive block, gradient, and statistical copolymers (terminal groups are omitted).

Figure I. 10 Scheme I. 6

 106 Figure I.10 Tc of diblock copolymer of PDEGMA and POEGA with different end groups and sequences. Copyright 2015. Reproduced with permission from the Wiley Periodicals, Inc.Ref.[131]

( 1 )( 2 )( 3 )

 123 Abbreviations: mPEGV: poly(ethylene glycol) methyl ether vinylphenyl, PAPy: poly(N-

PEO17

  Abbreviations: P(A-Pro-OMe): poly(N-acryloyl-L-proline methyl ester), P(A-Hyp-OH): poly(N-acryloyl-4-trans-hydroxy-L-proline), NAG: N-acryloylglycine, NAGSP: Nacryloylglycine spiropyran ester, SPB: sulfopropylbetaine, Bz: benzylamine, THF: tetrahydrofurfurylamine, PSBMA: poly(sulfobetaine methacrylate), PSPP: poly(3-(N-(3methacrylamidopropyl)-N,N-dimethyl) ammoniopropane sulfonate), PSB: polysulfobetaine, MPS: 3-(N-(3methacrylamidopropyl)-N,N-dimethyl) ammoniopropane sulfonate, DMAPMA: N-(3-(dimethylamino) propyl) methacrylamide, MPDSAH: N-(3-(methacryloylamino) propyl)-N,N-dimethyl-N-(3-sulfopropyl) ammonium hydroxide.

7 .Table I. 8

 78 Abbreviations: PLA: poly(DL-lactide), PVim: poly(N-vinylimidazole).

Table I. 9

 9 Morphological transition of LCST-LCST typed copolymers. a Morphological transition upon heating & Examples PNIPAM-b-PEAM, [140] PDMAEEOMA137-b-PEMAEEOMA78, [18] P(mPEGV466)18-b-PNIPAM60, [143] PEOVE-b-PMOVE, [128] PNIPAM115-b-PNAEAA230 [11] PNnPAM84-b-PEMAM42, [142] PAPyb-P(APi-co-APy), [144] PNIPAM-b-P(NIPAM-co-BMAAm), [145] PVCL315-b-P(MVA215-stat-VCL143), [104] PVCL132-b-P(VCL40-stat-VP172), [106] P(1-alt-5)6-b-P1)20, b [202] P(1-alt-4)26-b-P163, b [202] PNIPAM450-b-P(NIPAM244-co-HMAAm70), [98] P(nPA0.7-co-EAM0.3)-b-P(nPA0.4-co-EAM0.6), [146] P(MVC-co-VCL)-b-P(VCL-co-VP) [147] PMOVE58-b-PNIPAM170-b-PMOVE58, [150] PVCL132-b-P(VCL80-stat-VP344)-b-PVCL132 [106] PEO45-b-PNIPAM380-b-P(NIPAM423-co-HEAAm42), [152] PDEGA48-b-PDMAm150-b-PVCL113 [151] PNIPAM54-b-PDMAEMA46-b-PSt460, [149] P(mPEGV)32-b-PNIPAM170-b-PSt166 [148] a Effects of block sequence and structure on morphological transition of triblock copolymers upon heating are omitted. b 1: methoxytetraethylene glycol-4-vinylbenzyl ether, 5: N-(3-Trimethylsilyl) propylmaleimide, 4: N-decylmaleimide.

  Pro-OMe)27-b-P(A-Hyp-OH)73 (acidic water with NaCl),[156] PEO45-b-P(AAm-stat-AN) (H2O)[160] Tc > TCL PtBMA329-b-PVEA142 (methanol),[37] P(DEGMA60-stat-OEGMA40)27-b-PMAAm440 (H2O),[166] P(OEGMA-co-DEGMA)-b-P(MPS-co-DMAPMA) (H2O),[167] PdMMAEAPS-b-PDEAM (H2O),[69] P(AAm231-co-AN78)-b-PDMAEMA319 (H2O),[165] P(AM89-co-AN23)-b-PDMA475-b-PNIPAM57 (H2O),[170] PSPP430-b-PNIPAM200 (D2O),[164] PDMAEMA33-b-PSBMA36 (basic water),[162] PEO17-b-PNAGA99-b-PNIPAM63 (PBS),[168] PEO17-b-PNIPAM87-b-PNAGA83 (PBS)[168]

50 50

 50 Abbreviations: PVBA: poly(4-vinylbenzoic acid), PSSA: poly(4-styrenesulfonic acid), PVPA: poly(vinylphosphonic acid), PDPAEMA: poly(2-(diisopropylamino) ethyl methacrylate), P4VP: poly(4-vinylpyridine), P2VP: poly(2-vinylpyridine).

  effect on aggregates structure and size. Typical examples are poly(butadiene)-b-poly(Lglutamic acid) (PB-b-PGA) and poly(isoprene)-b-poly(L-lysine) (PI-b-PLys) (Figure I.11), in which micelles and vesicles are formed and their sizes display an increasing and decreasing tendency in pH range of 4 -7 and 6 -10, respectively. Whereas, in other pH ranges, no remarkable change in sizes is detected.[211][212][213]

Figure I. 11 .

 11 Figure I.11. Size of micelles and vesicles as a function of pH for PB-b-PGA and PI-b-PLys block copolymers having pH-responsive segments with different chain lengths (no addition of salt). Copyright 2007. Reproduced with permission from the Elsevier B. V. Ref.[213]

  Abbreviations: PIMA: poly(2-((3-(isopropylamino)-3-oxopropyl)(methyl)amino) ethyl acrylate), PEPyM: poly(N-ethylpyrrolidine methacrylate), PMAME: poly(N-methacryloyl-Lalanine 2-(dimethylamino) ethylamide), PMAEE: poly(N-methacryloyl-L-alanine 2-(diethylamino) ethylamide), PMAMP: poly(N-methacryloyl-L-alanine 3-(dimethylamino) propylamide), PMAEP: poly(N-methacryloyl-L-alanine 3-(diethylamino) propylamide), P(MEO1-DEAE-AM): poly(2-methoxyethyl 3-(N-(2-(diethylamino) ethyl) acrylamido) propanoate), P(DEAE-NIPAM-AM): poly(N-(2-(diethylamino) ethyl)-N-(3-(isopropylamino)-3oxopropyl) acrylamide), P(MA-iAsn-OH): poly(N-methacryloyl-L-β-isopropylasparagine).

  Morphological transition triggered by pH and temperature a & Examples PNIPAM-b-PVBA, [231] PNIPAM38-b-(PGMA48-graf-PGA9) [232] Star PNIPAM-b-(PDEAEMA)4, [233] PDEAEMA98-b-PNIPAM209, [234] PNIPAM-b-P4VP, [235] PPO33-b-PDEAEMA42, [236] PMOVE200-b-PAEVE50, [237] PNIPAM-b-(PEA-graf-P2VP), [238] POEGMA-b-P4VP, [239] P2VP-b-PNIPAM [240] a Polyacids are insoluble at low pH and soluble at high pH, while polybases are insoluble at high pH and soluble at low pH. Abbreviations: PAEVE: poly(primary amino groups), PEA: poly(ethyl acrylate).

Scheme 14 .

 14 Scheme 14. CO2-responisve mechanism.

  Abbreviations: CMA: coumarin methacrylate, PAD: poly((N-amidino) dodecyl acrylamide), PHIS: poly(histamine acrylamido), PHFBMA: poly(2,2,3,4,4,4-hexafluorobutyl methacrylate).

  Morphological transition triggered upon heating/cooling and CO2 treatment/removal & Examples PDEAEMA60-b-PNIPAM40 [254] PADS-b-PDMAEMA [255] Py-PCL-b-P(NIPAM-co-DMAEMA) [256] PEO45-b-P(NIPAM220-co-DEAEMA90) [137] PNIPAM-b-PCL-b-PDMAEMA [257] PEG45-b-P(AAm223-co-AN103)-b-PDEAEMA83* [258]*Thermoresponsive block with a UCST behavior. Abbreviations: PADS: N'-Propargyl-N,Ndimethylacetamidine modified poly(p-azidomethylstyrene), Py: pyrene group.

a

  Only catalyst and initiator are presented, other polymerization conditions like solvents, polymerization temperature, reaction time and post-modification can be referred to the corresponding references.

  Abbreviations: PSBMA: sulfobetaine modified poly(N,N-dimethylamino ethyl methacrylate).

[ 277 ]

 277 Scheme I.18 Tunable catalytic activity of AgNPs coated with PDEAEMA in reduction of pnitrophenol to p-aminophenol upon bubbling CO2/N2. Copyright 2017. Reproduced with permission from the Royal Society of Chemistry. Ref.[277]

(II. 2 II. 3 II. 3 . 1

 2331 such as microstructures, molecular weight, concentration, composition...) affecting phase transition behavior and self-organization of such (co)polymers solution upon stimuli treatment/removal are discussed. Meanwhile, a short introduction of synthetic methods (ATRP, RAFT polymerization) and applications is presented in the end of this chapter. Contents II.1 Introduction ..................................................................................................................... Synthesis and characterization of copolymers ............................................................. Formation of nanohybrids .............................................................................................. In situ formation .......................................................................................................... II.3.2 Coating of preformed AuNPs ..................................................................................... II.4 Conclusions .................................................................................................................... II.5 References ......................................................................................................................

(

  VCL) monomer only differs from N-vinylpyrrolidone (VP) by the inclusion of two additional methylene groups. Reversible addition-fragmentation chain transfer (RAFT) polymerization has recently made it possible to synthesize copolymers of VCL and VP with variable architectures and tunable thermoresponsive properties. [25, 27-29] Detrembleur and coworkers synthesized PVCL-b-P(VCL-stat-VP)-b-PVCL with adjustable hydration/dehydration

[ 27 ] 1 .Scheme II. 1

 2711 Scheme II.1 Synthesis of P(VCL-stat-VP)20k by RAFT/MADIX polymerization (synthesis was done by X. Zhao in IMRCP, Toulouse, France).Taking 1 H NMR spectrum of purified P(VCL75-stat-VP25) as an example (Figure II.1A), its composition can be calculated by integration area ratio of broad signal at 4 -4.4 ppm corresponding to the methine proton in VCL units and signal at 2.8 -3.5 ppm corresponding to

Figure II. 1

 1 Figure II.1 (A) 1 H NMR spectrum of P(VCL75-stat-VP25) in D2O and (B) SEC traces for P(VCL-stat-VP)20k with different compositions in DMF (containing LiBr) with a flow rate of 1 mL•min -1 ( 1 H NMR and SEC analyses were performed by X. Zhao in IMRCP, Toulouse, France).

  x a/[0.5(b+c)] %PVP = 100 x [0.5(b+c)-a]/[0.5(b+c)]

  P(VCL-stat-VP)20k at different (co)polymer concentrations (0.001, 0.01, 0.1 and 0.5 wt.%), the formation of AuNPs was detected by TEM and UV-vis measurements. Different colors of the colloidal solutions are observed in Figure II.2, which indicating that polymer concentration drastically modifies the particles growth. At the lowest polymer concentration (0.001 wt.%), a sharp surface plasmon band (SPB) is visible for all nanohybrids (blue curve in Figure II.3).

Figure II. 2

 2 Figure II.2 Effect of (co)polymer concentration and (co)polymer composition on in-situ formation of nanohybrids. The formation of AuNPs was induced by the addition of NaBH4 in NaAuCl4•2H2O in presence of P(VCL-stat-VP)20k at different concentrations ([NaBH4] = [Au]final = 5×10 -4 mol•L -1 . Photos of colloidal solutions were taken by H.H. Nguyen in IMRCP, Toulouse, France).

Figure II. 3 .

 3 Figure II.3. UV-vis spectra of nanohybrids at different (co)polymer compositions and (co)polymer concentrations detected five days after in-situ formation ([Au]final = 5×10 -4 mol• L -1 , [P(VCL-stat-VP)20k] = 0.001, 0.01, 0.1 and 0.5 wt.%. UV-vis spectra were performed by H.H. Nguyen in IMRCP, Toulouse, France).

  considered. As illustrated in Figure II.4A, an increase of the intensity of measured plasmon band with an increase of VP fraction in copolymer is observed. TEM analysis (Figures II.4B

  Figure II.4 (A)UV-vis spectra of nanohybrids detected five days after in-situ formation ([Au]final = 5×10 -4 molL -1 , [P(VCL-stat-VP)20k] = 0.01 wt.%, VP contents are 0, 25, 40, 50, 75, 90 and 100%), (B) TEM images for Au@PVCL, Au@P(VCL75-stat-VP25), Au@P(VCL50-stat-VP50) and Au@P(VCL10stat-VP90) and (C) Evolution of average size as a function of VP content (the line is only a guide for the eyes). (UV-vis spectra and TEM analyses were performed by H.H. Nguyen in IMRCP, Toulouse, France)

  30] Four different (co)polymer concentrations were used for each (co)polymer (final concentration equals to 10 -4 , 10 -3 , 5×10 -3 and 10 -2 wt.%). As illustrated in Figure II.5, all solutions remain stable in absence of NaOH or NaCl after coating AuNPs with P(VCL-stat-VP)20k (columns A1, B1, C1 and D1).

Figure II. 5

 5 Figure II.5 Colloidal stability of aqueous solutions of Au@P(VCL-stat-VP)20k observed at four different (co)polymer concentrations and different (co)polymer compositions (A) immediately (B) after 2 hours and (C) after 2 weeks after addition of NaOH (A2, B2, C2, D2, pHfinal = 10) and after addition of NaCl (A3, B3, C3, D3, [NaCl]final = 1 mol•L -1 ) compared to a control (A1, B1, C1, D1). (An: 10 -4 wt.%, Bn: 10 -3 wt.%, Cn: 5×10 -3 wt.%, Dn: 10 -2 wt.%, [Au]final = 2.5×10 -4 mol•L -1 ) Moreover, the average hydrodynamic diameters of Au@P(VCL-stat-VP)20k measured by DLS measurements are around 9 ± 2 nm (see Figure II.6), which is larger than that of bare AuNPs (5 ± 2 nm) and corresponds to colloidal solutions made of AuNPs surrounded by a polymer corona preventing aggregation through steric hindrance. Additionally, the evolutions

Figure II. 6

 6 Figure II.6 (A) Correlograms, (B) size distribution (number-averaged) and (C) corresponding averaged hydrodynamic diameter of AuNPs coated by P(VCL-stat-VP)20k copolymers at 25 o C (column B1 in Figure II.5, [Au]final = 2.5×10 -4 mol•L -1 , [(co)polymer] = 10 -3 wt.%).

Figure II. 5 )

 5 Figure II.5). As copolymer concentration raises to 10 -3 wt.%, the effect of copolymer composition on colloidal stability is clearly detected by column B2 in Figure II.5 and by evolution of absorbance spectra in Figure II.7, with an increase of VP content, the solution stabilization is weakened gradually. After two weeks, only Au@PVCL and Au@P(VCL75-stat-VP25) remain very weak stability, the nanohybrids in other cases flocculates. Further increasing copolymer concentration, the colloidal solution becomes more stable even after two weeks whatever copolymer used (see columns C2 and D2 in Figure II.5). The addition of NaCl shifts Au@P(VCL-stat-VP)20k stability towards higher copolymer concentration (columns A3, B3, C3 and D3 in Figure II.5). For a given copolymer concentration (i.e. 10 -3 wt.%), the system

Figure II. 7

 7 Figure II.7 UV-vis absorption spectra of nanohybrids at different copolymer composition between 400 and 800 nm (a) after two hours and (b) after two weeks detected after addition of NaOH (column B2, pHfinal = 10) and NaCl (column B3, ([NaCl]final = 1 mol•L -1 ) compared to a control (column B1). ([(co)polymer] = 10 -3 wt.%, [Au]final = 2.5×10 -4 molL -1 )

Figure II. 8

 8 Figure II.8 by measuring the absorbance of solutions at 520 nm between 20 and 70 °C as a function of the copolymer composition. Only Au@PVCL and Au@P(VCL75-stat-VP25) systems present a significant increase of absorbance induced by an increase of temperature (Figures II.8 and II.9A). Increasing VP content induces two main effects on thermoresponsive properties: (1) a shift of transition temperature to higher values as observed in Figure II.8 and (2) a lower variation of enthalpy during the phase transition. As a result, only nanohybrids coated by copolymers with VP content below 40% present thermoresponsive properties in solution at a chosen concentration. Additionally, only colloidal solution of Au@PVCL shows a significant change in the wavelength of the maximum absorbance when temperature increases from 20 to 70 °C (Figure II.9B) as previously observed. [27] Thus, increasing VP content in P(VCL-stat-VP)20k is detrimental to thermoresponsive property and to the aggregation of NPs.

Figure II. 8

 8 Figure II.8 Evolution of absorbance (an arbitrary unit was chosen) at 520 nm as a function of temperature for pristine AuNPs and AuNPs coated by different copolymers ([P(VCL-stat-VP)20k] = 2.5×10 -2 wt.%, [Au]final = 2.5×10 -4 mol• L -1 ). In addition, temperature change is likely to induce changes in the aggregation state of colloidal solutions. In order to evaluate the ability of different copolymers to effectively and reversibly stabilize AuNPs, the absorbance spectra at 20 °C are compared before and after temperature rises to 70 °C (Figure II.9C). The two homopolymer-based colloidal solutions Au@PVCL and Au@PVP show the smallest variation in absorbance and are therefore the least sensitive to temperature variation.

Figure II. 9

 9 Figure II.9 (A) Variation of absorbance observed at 70 °C compared to the one measured at 20 °C. (B) Variation of wavelength corresponding to the maximum of absorbance observed at 70 °C compared to the one measured at 20 °C. (C) Variation of absorbance observed at 20 °C before and after increasing temperature to 70 °C ([P(VCL-stat-VP)20k] = 2.5×10 -2 wt.%, [Au]final = 2.5×10 -4 mol• L -1 ).

  Figures II.10A and II.10Cshow the absorbance spectra of catalytic reaction system of nnitrophenol at different reaction time in the presence of Au@P(VCL75-stat-VP25) and Au@PVCL at 20 °C respectively.

Figure II. 10

 10 Figure II.10 UV-vis spectra of the reduction of p-nitrophenol to p-aminophenol by NaBH4 catalyzed by (A) Au@P(VCL75-stat-VP25) and (C) Au@PVCL at 20 °C. Plots of ln(A/A0) vs time for (B) Au@P(VCL75-stat-VP25) and (D) Au@PVCL at different temperatures ([p-nitrophenol] = 10 -4 mol•L -1 , [Au] = 5×10 -5 mol•L -1 , [NaBH4] = 3×10 -3 mol•L -1 , [(co)polymer] = 5×10 -3 wt.%).

Figure II. 11 .

 11 Results suggest that the catalytic activity increases with temperature until the cloud point is reached after which no catalytic efficiency is observed.

Figure II. 11

 11 Figure II.11 Pseudo-first order kinetic constant (kobs) as a function of temperature for Au@P(VCL75stat-VP25) and Au@PVCL ([p-nitrophenol] = 10 -4 mol•L -1 , [Au] = 5×10 -5 mol•L -1 , [NaBH4] = 3×10 -3 mol•L -1 , [(co)polymer] = 5×10 -3 wt.%).

Figure II. 12

 12 Figure II.12 (A) Plots of ln(A/A0) vs time for the reduction of p-nitrophenol by NaBH4 catalyzed by AuNPs stabilized by different statistical polymers at 20 °C and (B) corresponding pseudo-first order kinetic constant (kobs) as a function of polymer composition ([Au] = 5×10 -5 mol•L -1 , [P(VCL-stat-VP)20k] = 5×10 -3 wt.%, [p-nitrophenol] = 10 -4 mol•L -1 , [NaBH4] = 3×10 -3 mol•L -1 ).

III. 2 . 1

 21 Scheme III.1. Structures of P(BA-co-NIPAM) synthesized in this chapter.(i) Synthesis of PBA-b-PNIPAM diblock copolymers

Figures III. 1 ,

 1 Figures III.1, III.2 and III.3, respectively.

Figure III.1 1 H 3 in

 13 Figure III.1 1 H NMR spectra of (A) PNIPAM4k-b-PBA2k-b-PNIPAM4k and (B) PNIPAM2.5k-b-PBA5kb-PNIPAM2.5k in CDCl3. In the case of PNIPAM4k-b-PBA2k-b-PNIPAM4k, the signals at 4.0 ppm are attributed to the methylene in  position of the ester group of PBA block and isopropyl methine of PNIPAM block, the peaks at 0.9 ppm are attributed to methyl group in PBA, the signals of unreacted NIPAM are about 5.5 -6.0 ppm. According to the integrals of these special groups in 1 H NMR spectrum (Figure III.1A), the NIPAM conversion is calculated above 99%, and the molar ratio of NIPAM and BA is 4.37, suggesting the PNIPAM4k-b-PBA2k-b-PNIPAM4k was successfully synthesized. The same treatment method is used to calculate NIPAM conversion and molar ratio of NIPAM/BA in other cases, the detailed information is shown in Tables ES.2 and ES.3 in Experimental Section.

Figure III.3 1 H

 1 Figure III.3 1 H NMR spectra of (A) P(BA2k-stat-NIPAM8k), (B) P(BA1k-stat-NIPAM9k) and (C) P(BA0.5k-stat-NIPAM9.5k) in CDCl3. Number-average molecular weights (Mn) and dispersity (Ð) of all the copolymers were evaluated by SEC measurements (Figure III.4). The detailed information of all PBA precursors and BA/NIPAM copolymers is reported in Table III.1. In all cases, the Mn values are very close to theoretical expectations for a controlled RAFT/MADIX polymerization, which is in agreement with known values of transfer constants (Ctr) of BA and NIPAM to xanthate X1

Figure III. 4

 4 Figure III.4 SEC curves of (A) diblock, (B) triblock and (C) statistical copolymers in THF (copolymer concentration was 10 mg• mL -1 , eluent flow rate was 1 mL• min -1 ).

. 1 ,

 1 the dispersity values are close to 1.3 for PNIPAM and lie in the range of 1.3 -1.4 for PBA. By approximating at the end of polymerization process Đ to 1+1/Cex (Cex is interchain transfer constant), [24] the xanthate exchange can be considered as relatively slow in both cases (Cex ~ 3 in line with Ctr,X1 values) and slightly slower in the case of BA than NIPAM. Concerning these copolymers, their experimental Mn values are very close to theoretical estimations. Đ values of block copolymers tend to slightly decrease compared to that of PBA block precursor (1.16 < Đ < 1.40). Most importantly, as illustrated in the case of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k, the overlay of SEC chromatograms of PBA precursor and resulting diblock or triblock copolymers in THF shows that in both cases, PBA is successfully incorporated in the final copolymer (Figure III.5).

Figure III. 5

 5 Figure III.5 Size exclusion chromatograms (RI response) of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (red line) and PBA5k (blue line) in THF.

Figure III. 6 Figure III. 7 Figure III. 8 Figure III. 9

 6789 Figure III.6 Turbidimetry, DLS and DSC measurements of PNIPAM4k-b-PBA2k-b-PNIPAM4k solution. (A) Transmittance curves recorded at 500 nm as a function of temperature with a heating/cooling rate of 1 °C •min -1 . (B) Extrapolation of inflection points determined from turbidimetry curves at different heating/cooling rates. (C) Hydrodynamic diameter obtained from DLS measurements upon heating. (D) DSC thermograms recorded upon heating and cooling at a rate of 1 °C •min -1 . (Polymer concentrations used for turbidimetry, DLS and DSC measurements were 0.1, 0.1 and 1 wt.%, respectively)

  the case of PNIPAM4k-b-PBA2kb-PNIPAM4k Tc values equal to 27.7, 26.0 and 26.0 °C are obtained upon heating thanks to turbidimetry, DLS and DSC measurements respectively. It should be noted that for these polymers with low molecular weight, the study of thermal properties by using UV-visible spectroscopy leads to a systematic overestimation of Tc values compared to those obtained from DSC or DLS measurements, regardless of the studied polymer family. Such effect can be attributed to the fact that aggregates with sufficient size can be detected by these techniques. Thus, even as the dehydration of the polymer chain begins, as evidenced by DSC measurements, the formation of aggregates with sufficient size able to scatter light at a sufficient level requires a certain amount of time and/or greater dehydration level. Therefore, DSC was performed on the different families of copolymers in order to compare the Tc and corresponding enthalpy variations (H).Figure III.13 shows Tc values obtained by DSC upon heating or cooling for the different families of copolymers at a concentration of 1, 5 and 20 wt.%.

Figure III. 13

 13 Figure III.13 Cloud point temperatures Tc (peak maximum) obtained by DSC measurements on heating (red plain marks) or cooling (blue open marks) for PNIPAM homopolymer and statistical, diblock and triblock PNIPAM-based copolymers at a concentration of (A) 1, (B) 5 and (C) 20 wt.%. As can be seen in Figure III.13, it has to be noted that for most (co)polymers, there is no significant difference in Tc values measured at different concentrations. Only PNIPAM shows a significantly different value at 1 wt.% compared to the values assessed at 5 and 10 wt.% (i.e. 36, 32 and 32 °C respectively). Moreover, compared to PNIPAM homopolymer, incorporation of a hydrophobic monomer in the PNIPAM chain leads to a significant decrease in Tc values

  block density of the core, NA is Avogadro number. From this, average aggregation number Nagg = 163 and 405 are found for copolymer micelles of PNIPAM4k-b-PBA2k-b-PNIPAM4k and PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k respectively. By noting NA is the number of monomers of the hydrophobic block, the observed increase of Nagg is in good agreement with the expected scaling law Nagg  NA 2 . [26] The surface area per chain calculated from A c = 4πR core 2 /N agg gives values of 1.85 and 2.52 nm 2 respectively.

Figure III. 14 (

 14 Figure III.14 (A) Scattering intensity in absolute units (cm -1 ) of D2O solutions of (0.1 wt.%) PNIPAM4kb-PBA2k-b-PNIPAM4k (+) and PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (o) measured at 20 °C. Lines are the best fits to a model of polydisperse sphere with a Lognormal distribution. (B) Representative TEM micrograph of aggregates formed by PNIPAM4k-b-PBA2k-b-PNIPAM4k at 20 °C stained with uranyl acetate (TEM deposit was performed below Tc). (SANS measurement was done by N. Lauth-de Viguerie and A. Brûlet in LLB, Gif sur Yvette Cedex, France. TEM image was taken by H.H. Nguyen in IMRCP, Toulouse, France.)Diblock copolymers show the same tendency: an increase of size and aggregation number with an increase of BA content[13] with Nagg = 710 and 4800 respectively for copolymer micelles of PBA2k-b-PNIPAM8k and PBA5k-b-PNIPAM5k with a surface area per chain in the corona for the two micellar systems gives values of 1.13 and 1.10 nm 2 respectively. Thus, at 20 °C, both diblock and triblock structures enable the formation of micellar structures. For a given composition, these specific structures favor their solubility and are responsible for higher Tc values compared to the statistical microstructure. In addition, compared to diblock copolymers, triblock counterparts lead to smaller and less dense structures.

Figure III. 15 (

 15 Figure III.15 (A) Scattering intensity in absolute units (cm -1 ) of D2O solutions of (0.1 wt.%) PNIPAM4kb-PBA2k-b-PNIPAM4k (+) and PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (o) measured at 36 °C. Lines are the best fits to a model of polydisperse sphere with Gaussian distribution. (B) TEM image of aggregates formed above the cloud point for PNIPAM4k-b-PBA2k-b-PNIPAM4k (TEM deposit was performed above Tc, followed by a negative staining with uranyl acetate. SANS measurement was done by N. Lauth-de Viguerie and A. Brûlet in LLB, Gif sur Yvette Cedex, France. TEM image was taken by H.H. Nguyen in IMRCP, Toulouse, France.)

Figure III. 16

 16 Figure III.16 Photographs of phase states of PNIPAM4k-b-PBA2k-b-PNIPAM4k (20 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 20 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

  An initial visual assessment of the effect of temperature for different (co)polymer structures, compositions or concentrations was performed. Figure III.16 shows phase states of PNIPAM4k-b-PBA2k-b-PNIPAM4k aqueous solution with a concentration of 20 wt.% in temperature range from 20 to 40 o C.

Figure III. 17

 17 Figure III.17 Photographs of the observed phase transition for PNIPAM4k-b-PBA2k-b-PNIPAM4k triblock structure at a concentration of 20 wt.% as a function of temperature: transparent solution (TS) → opaque solution (OS) → opaque gel phase (OG) → dehydrated gel phase (DG).As shown in Figure III.17, below Tc, i.e. 26 °C, the transparent polymer solution looks like a free-flowing liquid independently of the concentration so that we name this phase as transparent solution (TS). As the solution is heated above the transition temperature, the solution rapidly becomes white and turbid but remain freely mobile. This phase is noted OS as opaque solution. Then heating more, an opaque gel phase (OG) appears: this gel phase is identified by gently tilting the vials[30] when no fluidity is visually observed on tilting after 5 min. As temperature increases, macrophase separation (synaeresis) with volume shrinkage by expelling water occurs and forms the final dehydrated gel phase (DG). The similar observations of PNIPAM4k-b-PBA2k-b-PNIPAM4k were made at different concentrations (5, 10 and 15 wt.%, see Figures III.18 -III.20).

Figure III. 19

 19 Figure III.19 Photographs of phase states of PNIPAM4k-b-PBA2k-b-PNIPAM4k (10 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 20 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

Figure III. 20 Figure III. 21

 2021 Figure III.20 Photographs of phase states of PNIPAM4k-b-PBA2k-b-PNIPAM4k (5 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 20 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state). To compare temperature-/concentration-dependent phase transition temperatures of different (co)polymer structures, the similar procedures were operated in other (co)polymer samples, the photographs of PBA2k-b-PNIPAM8k in concentration range from 5 to 20 wt.% are showed in Figures III.21 -III.24.

Figure III. 22

 22 Figure III.22 Photographs of phase states of PBA2k-b-PNIPAM8k (15 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 20 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

Figure III. 23

 23 Figure III.23 Photographs of phase states of PBA2k-b-PNIPAM8k (10 wt.% in water) as a function of

Figure III. 24 Figure III. 25

 2425 Figure III.24 Photographs of phase states of PBA2k-b-PNIPAM8k (5 wt.% in water) at 30, 32 and 34 o C (The sample was equilibrated in a dry box for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state). The photographs of phase states for PNIPAM10k in concentration range of 5 -20 wt.% are showed in Figures III.25 -III.28.

Figure III. 26

 26 Figure III.26 Photographs of phase states of PNIPAM10k (15 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 26 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

Figure III. 27

 27 Figure III.27 Photographs of phase states of PNIPAM10k (10 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 24 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

Figure III. 28

 28 Figure III.28 Photographs of phase states of PNIPAM10k (5 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 26 to 40 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state). Photographs of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k in concentration range of 5 -20 wt.% are shown in Figures III.29 -III.32.

Figure III. 30

 30 Figure III.30 Photographs of phase states of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (15 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 22 to 30 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

Figure III. 31

 31 Figure III.31 Photographs of phase states of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (10 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 22 to 28 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state).

Figure III. 32

 32 Figure III.32 Photographs of phase states of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (5 wt.% in water) as a function of temperature (Experiment was carried out in a dry box ranging from 22 to 28 o C at 2 o C intervals, the sample was equilibrated for 5 min at a given temperature before visual observation, then the same procedure was operated at higher temperature after sample recovered to transparent state). Based on these measurements, a phase diagram describing the behavior of aqueous polymer solutions as a function of concentration was established and compared to the ones of PBA2k-b-PNIPAM8k diblock copolymer (see Figure III.33).

Figure III. 33

 33 Figure III.33 Phase diagram of aqueous polymer solutions for PNIPAM4k-b-PBA2k-b-PNIPAM4k (A) and PBA2k-b-PNIPAM8k (B) as a function of concentration. Whereas for the homopolymer PNIPAM10k, the formation of gel is only observed at concentrations of 15 and 20 wt.% (Figure III.34), for the diblock and triblock structures gel formation occurred at lower concentrations. In all cases, those gelation concentrations are found

Figure III. 34 ,

 34 triblock structure of PNIPAM2.5kb-PBA5k-b-PNIPAM2.5k with a higher PBA content favors the formation of gel at lower concentration (down to 5 wt.%) and displays a highly pronounced synaeresis phenomenon. This first set of experiments enables us to evidence the effect of microstructure on the macroscopic behavior in concentrated solution.

Figure III. 34

 34 Figure III.34 Phase diagram of aqueous polymer solutions for PNIPAM10k (A) and PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (B) as a function of concentration.

Figure III. 35

 35 Figure III.35 Stress-dependent storage and loss moduli for (A) PNIPAM4k-b-PBA2k-b-PNIPAM4k and (B) PBA2k-b-PNIPAM8k at lower and higher temperatures. (Copolymer concentration was 20 wt.%, heating rate was 1 °C• min -1 , frequency was 1 Hz. Storage modulus G': filled marks, loss modulus G": empty marks, dephasing in blue marks. These measurements highlight a large linear viscoelastic region (LVR), showing that the moduli are not affected by stress amplitude changes up to at least 10 Pa for the gel phase. For solutions at 20 °C, the LVR is shorter, extending up to around 1-2 Pa.)

  PNIPAM10k hydrogels at concentration of 20 wt.% (60 Pa) (see Figure III.37).[12]

Figure III. 37 (

 37 Figure III.37 (A) Temperature-(heating rate was 1 o C• min -1 , frequency was 1 Hz, stress was 1 Pa), (B) frequency-(stress amplitude was 1 Pa) and (C) stress-dependent (frequency was 1 Hz) storage and loss moduli of PNIPAM10k solution. ([PNIPAM10k] = 20 wt.%, storage modulus G': filled marks, loss modulus G": empty marks, dephasing in blue marks.)

  chains. Because of this large hysteresis, cycling the triblock polymer solution from 20 to 31 °C gives a good reproducibility of the sol-gel transition temperature, but G' and G" values and cooling curves (gel-sol) are more variable (see Figure III.39). The variability may also be related to the synaeresis effect observed with triblock structure.

Figure III. 38 Figure III. 39

 3839 Figure III.38 Frequency-dependent storage and loss moduli of (A) PNIPAM4k-b-PBA2k-b-PNIPAM4k and (B) PBA2k-b-PNIPAM8k solutions. (Copolymer concentrations were 20 wt.%, heating rate was 1 °C• min -1 , stress amplitude was 1 Pa. Storage modulus G': filled marks, loss modulus G": empty marks, dephasing in blue marks.)

Figure III. 40

 40 Figure III.40 Cryo-SEM images of gel structures formed at 40 °C for (A) PNIPAM4k-b-PBA2k-b-PNIPAM4k, (B) PBA2k-b-PNIPAM8k, (C) PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k and (D) PBA5k-b-PNIPAM5k (Pore size distributions are given as insets).

(

  Scheme IV.1 LCST-type thermoresponsive polymers.

152

  Scheme IV.2 Effect of N-alkyl group in N-alkyl-substituted polyacrylamides on thermoresponsive properties in aqueous solution.Recently different families of homopolymers bearing a tertiary amine function grafted on poly((meth)acrylate)s and poly((meth)acrylamide)s main chains have been studied[13] as illustrated in Scheme IV.3. The presence of tertiary amine moieties exhibits pH-responsive characteristics due to their reversible protonation/deprotonation processes, and enables these polymers to combine thermo-and pH-responsive (soluble in acidic solution and insoluble in alkaline media) properties.[14] Depending on the nature of alkyl chains, these families of polymers present either pH or dual pH-and thermo-responsive properties.[15] Among them, poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) is the most commonly studied due to its commercially available monomer. Additionally, PDMAEMA is a weak polybase partially protonated in a physiological solution owing to the pKa of around 7.4. Thanks to the inherent cationic charge, the polymer has potential to be a gene transfer agent.[16]

  Scheme IV.4 PNIPAM, PDEAEAM and PNIPAM-b-PDEAEAM studied in this chapter.

5 .Scheme IV. 5

 55 Scheme IV.5 Synthetic routes of (a) monomer of DEAEAM, (b) PDEAEAM homopolymer and (c) PNIPAMn-b-PDEAEAMm (n/m values for block copolymers studied in this chapter are 2k/8k, 5k/5k and 8k/2k).The successful preparation of DEAEAM was confirmed by 1 H and13 C NMR spectra (see Figure IV.1), which are in good agreement with the results reported in the literature.[23]

Figure IV.1 1 H

 1 Figure IV.1 1 H and 13 C NMR spectra of DEAEAM in CDCl3. The successful polymerization of DEAEAM from PN5k macro-RAFT agent (synthetic route described in Experimental Section) is assessed from 1 H NMR experiments, in which the spectrum of PN5k-b-PD5k shows both characteristic peaks of PN5k and PD5k (Figure IV.2).

Figure IV. 4 5 .

 45 Figure IV.4 (A) 1 H NMR spectra of PN2k (bottom), PD8k (middle) and PN2k-b-PD8k (top) in D2O. SEC curves of PN2k, PN2k-b-PD8k (B) in DMF (containing 10 mM LiBr) and (C) in THF (containing 2 v% TEA) and (D) PD8k in THF (containing 2 v% TEA). (Eluent flow rate for all SEC measurements was 1 mL• min -1 ) By using the same synthetic methods, diblock copolymers of PN2k-b-PD8k and PN8k-b-PD2k were successfully prepared and characterized by 1 H NMR and SEC techniques as shown in Figures IV.4 and IV.5. Detailed information on synthesized diblock copolymers and their corresponding reference homopolymers are summarized in Table IV.1.

Figure IV. 5 Table IV. 1

 51 Figure IV.5 (A) 1 H NMR spectra of PN8k (bottom), PD2k (middle) and PN8k-b-PD2k (top) in D2O. SEC curves of PN8k, PN8k-b-PD2k (B) in DMF (containing 10 mM LiBr) and (C) in THF (containing 2 v% TEA) and (D) PD2k in THF (containing 2 v% TEA). (Eluent flow rate for all SEC measurements was 1 mL• min -1 )Table IV.1 Main characteristics of synthesized (co)polymers.

Scheme IV. 6

 6 Scheme IV.6 Structure and effect of temperature on the conformation of PN chains at pH 4. At pH 4, the measurement of Tc for 1 wt.% aqueous solutions of PNxk by DLS, turbidity and DSC measurements shows a non-linear increase of Tc from 16 to 29 °C when molecular weight increases from 2000 to 10000 g•mol -1 (Figure IV.6A).The observed tendency is mainly ascribed to the nature of terminal group. For PN2k, the hydrophobic -C12H25 tail group affects the solubility behavior and weakens the solvation of PN homopolymer in water, causing Tc of PN2k shifts toward lower temperature. This effect is highly pronounced for polymers with low molecular weight, however, it is much less remarkable when polymer chains are lengthened or

Figure IV. 6

 6 Figure IV.6 (A) Tc values of PN homopolymers in aqueous solutions determined by DLS, turbidimetry and DSC measurements upon heating (pH values of PN5k, PN8k and PN10k at concentration of 1 wt.% were 4.6, 4.3 and 4.3, respectively. PN concentration used for DLS, turbidity and DSC measurements were 1, 1 and 20 wt.%, respectively). (B) Aggregates size change and (C) transmittance change of PN5k as a function of temperature at different concentrations (pH ≈ 4, heating rate for turbidimetry measurement was 1 °C•min -1 ). As stated above, one extremity of the polymer bears a carboxylic function. It possesses a pKa value around 4.5 and therefore a modification of pH will induce a change of ionization/hydration state of this function and of the studied polymers. Consequently, a change in Tc of synthesized PN is expected. Thus, the thermoresponsive character of PN5k at different pH was studied by turbidimetry measurement (see Figure IV.7B). In pH range from 3 to 6, PN5k displays a clear LCST behavior, and its corresponding Tc value increases from 25.1 to 40.1 o C. Further increasing pH value, the transmittance at 70 °C no longer declines to 0 but approaches 44, 52 and 86% at pH 7, 8 and 9, respectively. When pH raises to 10, there is no detectable decrease in transmittance curve. In order to confirm the critical role of end group in the observed behavior, a PN homopolymer was synthesized from a different RAFT agent, namely 2-mercaptopropionic acid methyl ester O-ethyl dithiocarbonate (xanthate X1). No pHdependance of thermoresponsive behavior is observed for this homopolymer (Figure IV.7C), which confirms the critical role of end groups.

Figure IV. 7

 7 Figure IV.7 (A) Chemical structures of PN homopolymers synthesized by using different RAFT agents. Transmittance change of (B) PN5k and (C) PN10k-xanthate versus temperature at different pH values ([PN] = 1 wt.%, heating rate: 1 °C•min -1 ).

  performed as a function of temperature at two different pH values (4 and 10) and the behavior of PN5k was compared to that of PN10k-xanthate (without carboxylic acid end-group and long alkyl chain). At pH 10, PN10k-xanthate presents a transition at 35 °C that induces the formation of large aggregates (size around 500 nm) starting from aggregates around 70 nm. PN5k displays a completely different behavior. Indeed, it forms poorly defined nanoobjects in low temperature range (20 -32 o C) and forms small defined objects with an average diameter around 10 nm as temperature rises to 33 o C. (Figure IV.8A). Moreover, whatever the temperature (below or above Tc), a highly negative zeta potential is measured around -45 mV (Figure IV.8B), which is in agreement with nanoobjects bearing carboxylate function as an outer shell.

Figure IV. 8

 8 Figure IV.8 (A) Number-averaged size and (B) Zeta potential as a function of temperature for PN10kxanthate and PN5k at pH 4 and 10, respectively ([PN] = 0.1 wt.%). These measurements suggest the formation of micellar system stabilized by negatively charged carboxylate functions since increasing temperature results in contraction of PN chains as illustrated in Scheme IV.7. At pH 4, both PN10k-xanthate and PN5k present clear phase transitions, which can be judged by the aggregates size change as a function of temperature, large aggregates (size of 400 and 250 nm for PN10k-xanthate and PN5k, respectively) are formed when temperature increases to 60 o C (Figure IV.8A). As expected from partial protonation of carboxylate functions, zeta potential values around -10 mV is found for PN5k: this lower zeta potential does not enable to obtain stable colloidal structures and favored aggregation process upon heating.

Figure IV. 9

 9 Figure IV.9 Titration curve of (A) DEAEAM monomer and (B) PDEAEAM homopolymer (along with protonation degree). Transmittance change of aqueous solution of PD5k was then measured as a function of temperature (20 -70 °C) as pH increased from 3 to 10. No thermoresponsiveness is detected in the studied temperature range when pH is lower than 9. Interestingly for higher pH, deprotonation of tertiary amine promotes thermoresponsive properties of PD5k in water (see Figure IV.10A and top of Scheme IV.8). PD5k solution has a Tc equal to 60 °C at pH 9 then drops sharply to reach a value of 32 °C at pH 10.

Figure IV. 10

 10 Figure IV.10 Transmittance change of PD5k as a function of temperature (A) at different pH values and (B) at different concentrations (pH = 10). (C) Transmittance of PD homopolymers with different molecular weights at pH 10 versus temperature (PD concentration for all turbidimetry measurements was 1 wt.%).The effects of polymer concentration and molecular weight on thermoresponsive properties were then studied at pH 10 (above pKa). It is observed that an increase of concentration from 0.1 to 0.5 wt.% leads to a decrease of Tc from 37 to 32 °C with no further

Figure IV. 11 IV. 4 Scheme IV. 9

 1149 Figure IV.11 (A) Number-averaged size and (B) zeta potential of PD5k as a function of pH at 25 and 60 o C ([PD5k] = 0.1 wt.%).

Figure IV. 12 2 .Table IV. 2 a

 1222 Figure IV.12 Evolution of surface tension as a function of concentration for PN5k-b-PD5k solution (20 °C, pH ≈ 9).(i) Thermoresponsive behavior of PN5k-b-PD5k aqueous solution

Figure IV. 13

 13 Figure IV.13 At pH 10, (A) number-averaged size distribution of PN5k-b-PD5k as a function of temperature ([PN5k-b-PD5k] = 0.1 wt.%). (B) Transmittance change of PN5k-b-PD5k, PN5k and PD5k versus temperature ([(co)polymer] = 1 wt.%, heating rate: 1 o C• min -1 ).(ii) Mechanism of aggregation upon heating

Figure

  Figure IV.14B illustrates the evolution of T1 as a function of temperature. At 20 °C, all measured T1 values are above 750 ms, indicating the formation of large objects. When the temperature increases up to 40 °C, it is observed that T1 of protons in α position of amide function of PN block rapidly increases to reach 1600 ms. Restricted motion of polymer chains consecutive to a dehydration phenomenon might be responsible for this observation.Meanwhile, T1 of protons corresponding to PD block does not increase significantly. It seems that the dehydration mainly affects the mobility of PN block. Above 38 °C, all protons undergo a significant increase of T1 due to the formation of larger aggregates. The decrease of T1 observed for the proton in α position of amide function of PN block might be ascribed to the

Figure IV. 14 (

 14 Figure IV.14 (A) 1 H NMR spectra of PN5k-b-PD5k as a function of temperature at pH 10 (trioxane as internal standard with a chemical shift at 5.1 ppm and integral of 1 at whatever temperature studied). (B) Evolution of relaxation time (T1) as a function of temperature. (C) Evolution of integration of characteristic peaks in PN5k-b-PD5k relatively to the reference peak of trioxane. (D) Evolution of integration ratio between PN and PD block as a function of temperature. (T1 was measured by Y. Coppel in LCC, Toulouse, France) These T1 values were further considered to obtain 1 H NMR spectra in quantitative conditions and to determine the evolution of integrals of characteristic protons associated to PD (2.5 and 3.2 ppm) and PN (3.8 ppm) units relatively to the integral of trioxane chosen as a reference. As depicted in Figure IV.14C, the integral corresponding to PN units at 3.8 ppm remains roughly constant up to 32 °C, it then decreases slowly and a more pronounced decrease is observed above 38 °C. For PD block, a decrease is also evidenced above 32 °C but with no change of slope at 38 °C. The relative evolution of the integral ratio of PN and PD peak is represented in Figure IV.14D, a constant value is kept until 38 o C, after which a decrease is detected due to a more pronounced decrease of PN peaks than the one observed for PD. It is noteworthy that no change of chemical shifts is measured for the characteristic peaks of these two blocks in PN5k-b-PD5k. These results suggest that above 32 °C both PD and PN undergo progressive changes in their surroundings probably related to the progressive dehydration phenomenon. At 38 °C, an aggregation phenomenon occurs and promotes the formation of large aggregates in solution.

  Therefore, aggregation induces the formation of large aggregates from preexisting selfassemblies. To gain a further understanding of the underlying mechanism and of their kinetics, turbidimetry experiments were performed with different heating rates (Figure IV.15). It is found that Tc is measured at 35 °C at 0.2 o C•min -1 , and this value rises to 40 o C when heating rate increases to 5 o C•min -1 .

Figure IV. 15

 15 Figure IV.15 Transmittance change of PN5k-b-PD5k versus temperature at pH 10 at different heating rates ([PN5k-b-PD5k] = 1 wt.%, Tc determined by inflection point of transmittance curve). Moreover, at 60 °C, the hydrodynamic diameter of obtained aggregates goes on increasing as shown in Figure IV.16A over a period of 2 hours, starting from 130 to 180 nm. This implies that objects size depends strongly on kinetic consideration for aggregates formed above Tc and therefore on the way how experiments are performed (heating rate, equilibrating time…). This also suggests a possible reorganization of polymer/colloidal structure within the aggregates. This is confirmed by performing an additional scattering measurement in which the sample was heated directly at a chosen temperature starting from a solution at 20 °C. In this case, a hydrodynamic diameter of 188.5 ± 3.1 nm is found at 60 o C. Furthermore, Figure IV.16Billustrates the number-averaged hydrodynamic diameter and derived count rate by using a different heating way, in which a copolymer solution was heated and kept for 10 min at a chosen temperature then it was cooled down at 20 °C before performing heating process at another temperature. Measured hydrodynamic diameters are found around 250 nm above Tc and around 23 nm below Tc. Interestingly, at 20 °C this size increases slightly depending on the history of measurements illustrating the key role of reorganization of polymer/colloidal structure within the aggregates that occurs with characteristic timescale within minutes to hours. Noteworthy,

Figure IV. 16 (

 16 Figure IV.16 (A) Derived count rate and size change of PN5k-b-PD5k aggregates versus time at 60 o C. (B) Evolution of derived count rate and number-averaged size at different temperatures (PN5k-b-PD5k solution was heated and kept for 10 min at a chosen temperature, then it was cooled down to 20 o C before performing heating process at higher temperature). (pH = 10, [PN5k-b-PD5k] = 0.1 wt.%) (iii) Characterization of obtained aggregates below and above Tc

At 25 °C

 25 below Tc, both PN and PD segments are soluble in aqueous solutions and PN-b-PD comprises one hydrophobic terminal group (-C12H25) and a carboxylate function. TEM and cryo-TEM analysis (Figure IV.17) present spherical aggregates with an average diameter equal to 23.2 ± 5.7 and 34.3 ± 14.2 nm, respectively.

Figure IV. 17

 17 Figure IV.17 TEM, cryo-TEM images and Number-averaged size distribution of PN5k-b-PD5k (A) (C) (E) at 25 o C, (B) (F) at 60 o C and (D) at 50 o C. (pH = 10, 0.1, 0.5 and 0.1 wt.% of PN5k-b-PD5k solution for TEM, cryo-TEM and DLS measurements, respectively. TEM samples stained with 2 wt.% uranyl acetate solution, cryo-TEM measurements were done by S. Balor in CBI, Toulouse, France) At temperature above Tc, both PN and PD moieties shrink and become hydrophobic. Spherical objects are evidenced by TEM and cryo-TEM analysis with measured diameter equal to 92.8 ± 34.6 and 173.8 ± 76.1 nm, respectively. As stated above, the extent of aggregation depends strongly on kinetic consideration and on the history of colloid preparation. This suggests that micellar structures observed at 25 °C tends to aggregate. An estimation of hydrodynamic diameter of PN5k-b-PD5k objects detected by DLS measurement is around 190 nm, which is in good agreement with TEM results. Once again, the presence of carboxylate function can explain the observed limitation of aggregation process. Moreover, NMR results demonstrate that PN chains upon dehydration are present in more constrained environment than PD chains. Based on these analyses, the morphologies of PN5k-b-PD5k aggregates below and above Tc at pH 10 are proposed in Scheme IV.10.

Figure IV. 19

 19 Figure IV.19 Evolutions of derived count rate and number-averaged size distribution of PN5k-b-PD5k as a function of temperature ([PN5k-b-PD5k] = 1 wt.%, pH = 4). The evolution of transmittance as a function of temperature for PN5k-b-PD5k, PN5k and PD5k at pH 4 is shown in Figure IV.20. Whereas PN5k homopolymer has a Tc at 26 o C, no transmittance change of reference PD5k takes place in the studied temperature range. Indeed, PD5k is protonated and no more thermoresponsive. In the case of PN5k-b-PD5k, a two-step transmittance decrease occurs starting at 23 o C with the first inflection point of 29 o C (Tc,1) and the second one at 39 o C (Tc,2).

Figure IV. 20 (

 20 Figure IV.20 (A) Transmittance change of PN5k-b-PD5k, PN5k and PD5k at pH 4 as a function of temperature ([(co)polymer] = 1 wt.%, heating rate:1 o C•min -1 ). (B) Evolution of zeta potential as a function of temperature for PN5k-b-PD5k at pH 4 ([PN5k-b-PD5k] = 0.1 wt.%).The first transition at 29 °C might come from the thermoresponsive character of PN segment. Above Tc,1, PN chains in PN5k-b-PD5k collapse, inducing a reorganization of the colloidal structures formed at room temperature. With an increase of temperature, zeta potential is measured with an increasing tendency, which is in good agreement with a reorganization to

Figure IV. 21 (

 21 Figure IV.21 (A) 1 H NMR spectra of PN5k-b-PD5k as a function of temperature at pH 4 (trioxane as internal standard with a chemical shift at 5.1 ppm and an integral of 1 at whatever temperature studied). (B) Evolution of relaxation time (T1) of characteristic peaks in PN5k-b-PD5k as a function of temperature. (C) Evolution of integration of characteristic peaks in PN5k-b-PD5k relatively to the reference peak of trioxane. (D) Evolution of integration ratio between PN and PD block as a function of temperature. ([PN5k-b-PD5k] = 1 wt.%, T1 was measured by Y. Coppel in LCC, Toulouse, France) Figure IV.21B illustrates the evolution of T1 as a function of temperature. At 20 °C, all measured T1 values are above 600 ms, indicating the formation of large objects. When the temperature increases up to 50 °C, T1 of protons corresponding to PN increases. Restricted motion of polymer chains consecutive to a dehydration phenomenon and formation of larger objects might be responsible for this observation. At the same time, T1 of protons corresponding to PD block does not increase to such an extent. The increase of temperature seems to affect

Figure IV. 22 (

 22 Figure IV.22 (A) Transmittance change as a function of temperature with different heating rates, (B) number-averaged size change as a function of time at 20, 30, 45 and 60 o C for PN5k-b-PD5k and (C) evolution of number-averaged size at different temperatures (PN5k-b-PD5k solution was heated and kept for 10 min at a chosen temperature, then it was cooled down to 20 o C before performing heating process at higher temperature). (pH = 4, 1 and 0.1 wt.% of PN5k-b-PD5k solution for turbidimetry and DLS measurements, respectively) As already shown at pH 10, the size of obtained aggregate upon heating depends strongly on kinetic phenomenon due to reorganization of polymer/colloidal structure within the aggregates that occurs with characteristic timescale within minutes to hours (Figure IV.22C).

5 a

 5 preparation and equilibrating time. Measured number-averaged hydrodynamic diameters are 25.8 ± 9.4, 77.4 ± 8.5 and 200.3 ± 4.5 nm at 25 °C (T < Tc,1), 30 °C (Tc,1 < T < Tc,2) and 60 °C (T > Tc,2) (Table IV.4 and Figure IV.23F)Table IV.4 PN5k-b-PD5k aggregates size at different temperatures determined by TEM, cryo-TEM and DLS measurements.pH T (°C) TEM (d. nm) cryo-TEM (d. nm) DLS (d. nm) Measured at 50 °C. b Obtained from number-averaged size distribution. c Not determined. (0.1, 0.5 and 0.1 wt.% of PN5k-b-PD5k solution for TEM, cryo-TEM and DLS measurements, respectively). At 25 °C, as evidenced by TEM analysis (or cryo-TEM image, see Figures IV.23A and IV.23D), PN5k-b-PD5k polymer chains self-organize into uniform spherical aggregates with diameter of 23.1 ± 5.2 nm (or 31.4 ± 12.4 nm). This diameter is almost equal to the one of aggregates formed at pH 10. Whereas a carboxylic form is present on one hand, protonation of PD chains enables to ensure a good colloidal stability in solution. At 30 °C above Tc,1, PN chains start to collapse due to the dehydration phenomenon. However, PD block still maintains hydrophilic property and cationic character. As shown in TEM images (Figure IV.23B), PN5k-b-PD5k assembles into flower-like micelles with adiameter equal to 30.4 ± 8.9 nm. These structures can be issued either from a partial aggregation of previous ones formed at 25 °C or from a rearrangement of polymer chains in a core-shell structure with a core of hydrophobic -C12H25 end group and a shell of partially dehydrated PN block and hydrated cationic PD segment.When temperature goes up to temperature higher than Tc,2, larger spherical aggregates are formed (Figures IV.23C and IV.23E, diameter equal to 125.6 ± 38.9 nm and 159.5 ± 73.6 nm determined by TEM and cryo-TEM, respectively). These structures result from aggregation of previous ones and/or a more pronounced phase separation between PN and PD blocks.

Figure IV. 23

 23 Figure IV.23 At pH 4, TEM, cryo-TEM images (A) (D) at 25 o C, (B) at 30 o C, (C) at 60 o C and (E) at 50 °C. (F) Number-averaged size distribution of PN5k-b-PD5k aggregates at different temperatures. (0.1, 0.5 and 0.1 wt.% of PN5k-b-PD5k solution for TEM, cryo-TEM and DLS measurements, respectively. TEM samples stained with 2 wt.% uranyl acetate solution, cryo-TEM measurements were done by S. Balor in CBI, Toulouse, France) From the results obtained in this section, a schematic illustration of morphologies of PN5kb-PD5k formed at pH 4 under different temperatures is proposed as shown in Scheme IV.12.

Figure IV. 26

 26 Figure IV.26 TEM images and number-averaged size distribution of PN2k-b-PD8k and PN8k-b-PD2k at 25 and 60 o C. PN2k-b-PD8k: (A) 25 o C, (B) 60 o C, (C) number-averaged size distribution. PN8k-b-PD2k: (D) 25 o C, (E) 60 o C, (F) number-averaged size distribution. (pH = 10, [PN-b-PD] = 0.1 wt.%, TEM samples stained with 2 wt.% uranyl acetate solution)

  PN2k-b-PD8k and PN5k-b-PD5k present two transition temperatures, which induce the formation of larger aggregates with a PD positively charged outer shell. At pH 10, PN and PD block are both thermoresponsive. PN-b-PD solutions have only one single transition point

  Scheme V.3 Summary of dual thermo-and CO2-responsive homopolymers. (PDEAEAM: poly(N,Ndiethylamino ethyl acrylamide,[2] PEPyAM: poly(N-ethylpyrrolidine acrylamide),[3] PMAEE:

Figure V. 1

 1 Figure V.1 (A) Changes in system pH and protonation degree of PD5k solution in one cycle and (B, C) in two cycles upon alternate bubbling CO2/N2 ([PD5k] = 0.1 wt.%, gas flow rate was 2 mL•min -1 ).

  Figures V.1B and V.1C), it is shown that PD5k over alternate treatment with CO2/N2 exhibit good reversibility with at least two cycles. The products of reaction of PD homopolymer with CO2 at 25 °C was studied by 1 H NMR spectra. As shown in Figure V.2B, before addition of CO2, PD5k polymer presents three peaks at 3.32, 2.64 and 1.07 ppm corresponding to -CH2CH2N(CH2CH3)2, -CH2CH2N(CH2CH3)2

Figure V. 2

 2 Figure V.2 (A) Chemical reaction of PD5k with CO2 in water. (B)1 H and (C)13 C NMR spectra of PD5k in D2O recorded at 25 o C upon alternate exposure to CO2/N2 (PD5k concentration for NMR experiments was 1 wt.%, gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively.).

[ 2 ]Figure V. 3

 23 Figure V.3 Plots of (A) transmittance and (B) aggregates size versus temperature for PD5k aqueous solution before, after bubbling CO2 and after bubbling N2. ([PD5k] = 1 wt.%, heating rate for turbidimetry measurements was 1 o C• min -1 , gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively.) CO2-switchable thermoresponsiveness of PD5k was further analyzed by DLS measurements as shown in Figure V.3B. In the initial PD5k solution, a change of measured hydrodynamic diameter is observed at 33 o C (Tc), which is related to the shrinkage of PD5k units and hydrophobic association among intermolecular chains. Measured size goes on increasing upon heating up to 60 o C, then a precipitation takes place when larger aggregates are formed.

Figure V. 4

 4 Figure V.4 (A) Chemical reaction of PN5k-b-PD5k with CO2 in water, (B) 1 H NMR spectra of PN5kb-PD5k in D2O recorded at 25 o C upon alternate bubbling CO2/N2. (PN5k-b-PD5k concentration for NMR experiments was 1 wt.%, gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively.) To confirm this, CO2-responsiveness of PN5k-b-PD5k was analyzed by 1 H NMR spectra at room temperature (Figure V.4). The site of interaction between CO2 and PN5k-b-PD5k are evidenced in Figure V.4B. Chemical shifts of -CH2CH2N(CH2CH3)2, -CH2CH2N(CH2CH3)2 and -CH2CH2N(CH2CH3)2 in PD5k block move from 3.33, 2.65 and 1.08 ppm to 3.58, 3.28 and 1.33 ppm, respectively upon 10 min CO2 bubbling, and subsequently return to 3.43, 2.87 and 1.15 ppm, respectively after bubbling N2 for 30 min. Moreover, no chemical shift of signals at 3.89 and 1.15 ppm corresponding to -CH(CH3)2 and -CH(CH3)2 in PN5k is observed, which means CO2 only reacts with PD block to generate ammonium bicarbonate and has no effect on property of PN block. It has to be noted that upon alternate exposure to CO2/N2, PN5k-b-PD5k solution undergo a pH change: in the absence of CO2, system pH of PN5k-b-PD5k solution is around 10, then decreases to 6 upon CO2 aeration and comes to 8.5 after bubbling N2.

Figure V. 7 Scheme V. 6 V. 4

 764 Figure V.7 (A-C) TEM images and (D) number-averaged hydrodynamic size distribution of PN5k-b-PD5k before, after CO2 treatment and after exposure to N2 at 60 o C. ([PN5k-b-PD5k] = 0.1 wt.%, gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively. TEM samples stained with 2 wt.% uranyl acetate solution.) In presence of CO2, PN block is not affected and keeps its thermoresponsive property, whereas PD chains are protonated, which makes PD block no longer thermoresponsive in the studied temperature range. As temperature rises to 60 o C (above Tc), PN chains collapse and become hydrophobic, while PD chains remain good solubility. Therefore, flower-like micelles are formed with -C12H25 core, PN shell and PD corona. Moreover, the size of such aggregates (35.1 ± 7.4 nm) is smaller than that formed before CO2 treatment at the same temperature (Figure V.7B). This result is also confirmed by DLS analysis, in which hydrodynamic diameters of aggregates before and after exposure to CO2 are 188.5 ± 3.1 and 174.6 ± 4.5 nm, respectively. Upon bubbling N2, PD block regains thermoresponsiveness, as temperature increases above Tc, both PN and PD chains shrink. Spherical micelles cluster with large diameter (61.6 ± 13.5 nm) are formed (Figure V.7C). This value is smaller compared to the initial size (92.8 ± 34.6 nm) and it is confirmed by DLS results (hydrodynamic diameter of 188.5 ± 3.1 and 166.3 ± 4.9 nm obtained before bubbling CO2 and after treatment with N2, respectively) (see Figure V.7D).

Figure V.8 1 H

 1 Figure V.8 1 H NMR spectra of (A) PN2k-b-PD8k and (B) PN8k-b-PD2k in D2O recorded at 25 o C upon alternate bubbling CO2/N2. ([PN-b-PD] = 1 wt.%, gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively.) As shown in Figure V.8, upon alternate bubbling CO2/N2, chemical shifts of -CH(CH3)2 and -CH(CH3)2 in PN block remain around 3.9 and 1.15 ppm and are not influenced by CO2 treatment/removal. Whereas proton peaks of -CH2CH2N(CH2CH3)2, -CH2CH2N(CH2CH3)2 and -CH2CH2N(CH2CH3)2 in the case of PN2k-b-PD8k shift from 3.33, 2.66 and 1.08 ppm to 3.56, 3.26 and 1.32 ppm after 10 min exposure to CO2 and return to 3.41, 2.87 and 1.16 ppm as N2 is bubbled for 30 min. These signals in 1 H NMR spectra of PN8k-b-PD2k at 3.38, 2.73 and 1.15 ppm undergo a similar change under the same conditions, CO2 treatment causes a downfield shift (3.57, 3.27 and 1.3 ppm) and N2 aeration leads PD signals almost recover to initial positions (3.42, 2.9 and 1.15 ppm).

Figure V. 9 Table V. 1 a

 91 Figure V.9 Plots of transmittance for (A) PN2k-b-PD8k and (B) PN8k-b-PD2k aqueous solution before, after bubbling CO2 and after bubbling N2. ([PN-b-PD] = 1 wt.%, gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively.)

Figures V. 10

 10 Figures V.10 and V.11 present TEM and DLS analyses of PN2k-b-PD8k and PN8k-b-PD2k at 25 and 60 °C of the aggregates present in solution before, after exposure to CO2 and after bubbling N2. Detailed aggregates sizes of PN-b-PD under different conditions are summarized in Table V.2.

Figure V. 10

 10 Figure V.10 (A-C, E-F) TEM images and (D, H) number-averaged hydrodynamic size distribution of PN2k-b-PD8k before, after bubbling CO2 and after bubbling N2 at different temperatures. (A): before bubbling CO2, 25 o C, (B): after bubbling CO2, 25 o C, (C): bubbling N2, 25 o C, (E): before bubbling CO2, 60 o C, (F): before bubbling CO2, 60 o C, (G) before bubbling N2, 60 o C. ([PN2k-b-PD8k] = 0.1 wt.%, gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively. TEM samples stained with 2 wt.% uranyl acetate solution.)

  block. Deprotonation state can be almost recovered upon bubbling N2. To test the reversibility of CO2/N2 responsiveness, PN-b-PD solutions were repeatedly treated with alternate bubbling CO2/N2. The change of chemical shift of characteristic proton peaks in PD block was recorded by NMR experiments. As shown in Figure V.12A, only chemical shifts of p, qr and s signals in PN5k-b-PD5k shift toward downfield after CO2 treatment, then shift toward upfield and almost return to initial positions as CO2 is removed by bubbling N2. Meanwhile, pH of PN5k-b-PD5k solution decreases and increases after CO2 and N2 treatment, respectively. This suggests that PN5k-b-PD5k exhibits a good reversibility with a minimum of 7 cycles. The same phenomenon is also observed in other two PN-b-PD block copolymers whatever PN content (see Figures V.12C -V.12F).

Figure V. 12 V. 6 Conclusions

 126 Figure V.12 Changes of chemical shifts and system pH of (A, B) PN5k-b-PD5k, (C, D) PN2k-b-PD8k and (E, F) PN8k-b-PD2k at 25 o C upon alternate bubbling CO2/N2 for 7 cycles. ([PN-b-PD] = 1 wt.%, gas flow rate was 10 mL•min -1 , 10 and 30 min for bubbling CO2 and N2, respectively.)V.6 Conclusions

8 ES- 8

 88 Scheme ES.2 Synthesis of bis-xanthate X2.As shown in Scheme ES.2, 1.7246 g potassium O-ethylxanthate was added by fractions to a solution of diethyl 2,5-dibromoadipate (1.937 g, 5.38 mmol) in 20 mL anhydrous acetonitrile at 5 °C during 30 min. Then the mixture was stirred 2 h at 5 °C, at which reaction was complete (monitored by TLC). After evaporation of acetonitrile, the residue was dissolved in diethyl ether and washed with water. The organic phase was dried over anhydrous MgSO4, filtered and evaporated under vacuum to afford desired bis-xanthate X2 (2.25 g, yield: 94%) as a crystallized solid. Rf = 0.80 (CH2Cl2).1 H NMR (300 MHz, CDCl3, 25 °C): δH 4.66 (q, J = 7 Hz, 4H, -SCS-OCH2CH3); 4.42-4.38 (m, 2H, -CH2CHCOO-); 4.23 (q, J= 7 Hz, 4H, -OCOCH2CH3); 2.17-1.97 (m, 4H, -CHCH2-); 1.44 (t, J = 7 Hz, 6H, -SCS-OCH2CH3); 1.29 (t, J = 7 Hz, 6H, -COOCH2CH3).13 C NMR (75 MHz, CDCl3, 25 °C ): δ 211.6 (-SCS-); 170.3 (-OCO-); 70.5 (-SCS-OCH2CH3); 61.9 (-COOCH2); 51.9 (-CHCOO-); 28.8 (-CH2CH-); 14.2 (-COOCH2CH3); 13.7 (-SCS-OCH2CH3).

10 ES- 10

 1010 Scheme ES.4 Synthesis of PNIPAM-b-PBA-b-PNIPAM by RAFT/MADIX polymerization (synthesis was performed by J.S. Behra and N. Lauth-de Viguerie in IMRCP, Toulouse, France).

  Scheme ES.5 Synthesis of P(BA-stat-NIPAM) by RAFT/MADIX polymerization. P(BA-stat-NIPAM) copolymers were synthesized using xanthate X1 as RAFT agent (seeScheme ES.5). P(BA-stat-NIPAM) was prepared as follows (Table ES.3): Into an argon-filledSchlenk flask with a magnetic bar, a mixture of xanthate X1, AIBN, BA and NIPAM dissolved in 1,4-dioxane was added under argon. The flask was degassed via four cycles of freeze-pumpthaw and then placed in an oil bath at 75 °C. After 9 h, the reaction was terminated upon exposure to air and the flask was cooled rapidly with liquid nitrogen. Solvent was removed by evaporation under vacuum to obtain the white powder.

- 1 . 16 ES- 16

 11616 For (co)polymers aqueous solution, cloud point temperatures (Tc) of 1, 5 and 20 wt.% sample solutions were determined by using DSC measurements. Solution samples were sealed in impermeable crucibles of 120 µL. Tc values were estimated at the top of observed peaks on DSC thermograms when temperature decreased/increased at different rates: 5, 4, 3, 2 and 1 °C•min -1 , and finally extrapolated to 0 °C•min -1 . The variation of enthalpy was measured at a heating rate of 1 °C•min -1 .ES-Experimental SectionES.3.4 Turbidimetry measurementTransmittance of (co)polymer aqueous solutions at 500 nm with increasing temperature was recorded by a Cary 100 Bio spectrophotometer with 4 cycles at different heating/cooling rates (0.5, 1, 2.5 and 5 °C•min -1 ). Cloud points were calculated from the value obtained by extrapolation to 0 °C•min -1 of inflexion point on each transmittance curve at different rates.Three independent measurements were performed for each sample. ES.3.5 Dynamic Light Scattering (DLS) DLS measurements were carried out at different temperatures on a Malvern Instrument Nano-ZS equipped with a He-Ne laser (λ = 633 nm). Samples were introduced into cells (pathway: 10 mm). The reported apparent equivalent hydrodynamic diameter, Dh, is obtained by analysing measured correlation function via non-negative least square algorithm and using the Stokes-Einstein equation. Tc values were obtained by the inflection points (or onset temperature, where aggregates size start to change) of hydrodynamic size change curve as a function of temperature.ES.3.6 Visual AssessmentIn Chapter III, the phase state of polymer solutions as a function of temperature and concentration was visually assessed. This experiment was carried out in a dry box ranging from 20 to 40 o C with 2 o C intervals, the sample was equilibrated for 5 min at each temperature before visual observation. Then the same procedure was performed at higher temperature as sample recovered to transparent state.ES.3.7 Rheological measurementIn Chapter III, the rheological measurements were performed on an AR1000 rheometer from TA instruments in cone plate configuration (diameter 2 cm, 2° angle) equipped with a Peltier plate. An oscillatory stress with an amplitude of 1 Pa and frequency of 1 Hz was applied to the sample for viscoelastic measurements. With these settings, the variations of the storage modulus G' and the loss modulus G" along with temperature were monitored by applying a continuous linear temperature ramp at 1 °C•min -1 . The inflection point was selected as phase transition temperature.ES.3.8 Cryo-Scanning Electron Microscopy (cryo-SEM)In Chapter III, cryo-SEM images were performed on FEG FEI Quanta 250 microscope (Japan). (Co)polymer solution was preheated and underwent sol-to-gel transition before being frozen in nitrogen slush at -220 °C. The frozen sample was transferred under vacuum in the cryo-fracture apparatus (Quorum PP3000T Cryo Transfer System) chamber where it was fractured at -145 °C. After a sublimation step at -95 °C during 30 min, the sample was introduced into the microscope chamber at -145 °C, operating at 5 kV accelerating voltage.

18 ES- 18

 1818 by a cryogenic sample holder to the microscope and imaged at -178 °C. Adequate phase contrast was obtained at a nominal underfocus of 3-15 μm. (cryo-TEM measurements were performed by S. Balor in CBI, Toulouse, France) ES-Experimental Section ES.3.11 Small Angle Neutron Scattering (SANS) In Chapter III, SANS experiments were performed with PACE spectrometer on Orphé e reactor. Polymer solutions in D2O solvent were put inside quartz cells of 2 mm gap and measured at 20 °C and 40 °C. Different spectrometer configurations were used: a neutron wavelength () of 7Å with a sample to detector distance of 3 m to obtain intermediate q value

  solutions have been fitted using SASView software (http://sasview.org) to the model of polydisperse sphere (radius R) using a Gaussian distribution of radius (σR) and taking into account for each spectrometer configuration the corresponding resolution function. For triblock at 20 °C, the best fit radii were very small (3 nm) and the distribution very large (σR  2-3). The curves of triblock at 20 °C were also fitted to the model of polydisperse sphere but with a lognormal distribution (an asymmetric distribution compared to the Gaussian one) in order to obtain more reasonable values of fit parameters. (SANS experiments were performed by A.Brûlet and N. Lauth-de Viguerie in LLB, Gif sur Yvette Cedex, France)ES.3.12 Determination of pKaIn Chapter IV, prior to measurement, the pH of (co)polymer solution (0.01 M) was calibrated by HCl solution (0.1 M), then the solution was titrated with NaOH solution (0.1 M) and its pH was monitored continuously by pH meter until pH did not change. The pKa value was determined by the inflection point of pH curve as a function of NaOH concentration.

(II. 3 II. 4

 34 RMN), chromatographie d'exclusion sté rique (SEC) et calorimé trie diffé rentielle à balayage (DSC). Sché ma II.1. Synthè se de P(VCL-stat-VP) par polymé risation RAFT/MADIX. II.2 Croissance et stabilité des AuNPs Pour é tudier la stabilisation, les proprié té s optiques et catalytiques des nanohybrides formé s, deux mé thodes, comme indiqué dans le Sché ma II.2, ont é té adopté es pour obtenir des nanohybrides: (1) la formation in situ et (2) le revê tement d'AuNPs pré formé s. Sché ma II.2. Deux voies de synthè se utilisé es pour la formation de nanohybrides (formation in situ et revê tement de nanoparticules pré formé es).Les effets de la concentration et de la composition du polymè re sur la croissance in situ des AuNPs ont é té mis en é vidence par la couleur de la solution colloï dale, le microscope é lectronique à transmission (MET) et les mesures de spectroscopie UV-visible. Il est montré que l'augmentation de la concentration en polymè re a conduit à la couleur de la solution colloï dale passé e du brun au jaune pâ le, qui s'accompagnait d'une diminution progressive de l'intensité de la bande de plasmon de surface, suggé rant que la concentration en polymè re a considé rablement modifié la croissance des AuNPs. De plus, une augmentation de l'intensité de la bande de plasmon mesuré e avec une augmentation de la fraction VP dans le copolymè re a é té observé e. L'analyse MET a confirmé que la tendance observé e est lié e à une augmentation progressive de la taille moyenne de Au@P(VCL-stat-VP)20k formé lorsque la teneur en VP augmente. Les diffé rents copolymè res ont les mê mes groupes terminaux, ainsi les diffé rences observé es ne peuvent ê tre attribué es qu'à une diffé rence de composition: une teneur en VCL plus é levé e conduisant à un meilleur contrôle de la croissance des NPs. ix Ré sumé de thè se ix L'effet de la composition de copolymè re sur la stabilisation colloï dale d'une solution de particules (pré paré es en enrobant des AuNPs pré formé es avec une quantité choisie de chaque polymè re) soumise à une augmentation du pH ou de la force ionique est ensuite é valué aprè s addition de solution de NaOH ou de NaCl. Un changement de couleur progressif lié à la modification de la bande plasmonique des particules due à des phé nomè nes d'agré gation ou de sé dimentation traduit une faible stabilité colloï dale. L'augmentation de la concentration en polymè re permet d'augmenter la stabilité des AuNPs vis-à -vis de la modification du pH ou de l'ajout de sel en raison d'un encombrement sté rique plus é levé . De plus, pour une concentration choisie, PVCL favorise les NPs avec une stabilité colloï dale lé gè rement supé rieure. Thermoré activité des nanohybrides L'effet de la tempé rature sur les maté riaux hybrides obtenus est ensuite é valué en mesurant l'absorbance des solutions à 520 nm entre 20 et 70 °C en fonction de la composition du copolymè re. Seuls les systè mes Au@PVCL et Au@P(VCL75-stat-VP25) pré sentent une augmentation significative de l'absorbance induite par l'augmentation de la tempé rature, indiquant que les nanohybrides revê tus de polymè res avec une teneur en VP infé rieure à 40 % pré sentent des proprié té s thermosensibles en solution à une tempé rature choisie. concentration. Efficacité catalytique des nanohybrides Les performances catalytiques de tous les systè mes Au@P(VCL-stat-VP)20k ont é té testé es à diffé rentes tempé ratures (20, 30, 40, 50, 60 et 70 °C) dans la ré duction du p-nitrophé nol en paminophé nol dans l'eau en utilisant NaBH4 comme le montre la Figure II.1. Les constantes de vitesse observé es (kobs) pour toutes les ciné tiques ont é té extraites de la relation liné aire entre ln (At/A0) en fonction du temps t en supposant une ciné tique de pseudo premier ordre.

Figure II. 1 .

 1 Figure II.1. (A) Spectres UV-vis à 20 o C, (B) Tracé de ln(A/A0) en fonction du temps et (C) Constante ciné tique de pseudo-premier ordre (kobs) en fonction de la tempé rature dans la ré duction du p-nitrophé nol en p-aminophé nol par NaBH4 catalysé par Au@P(VCL75-stat-VP25) (la ligne rouge n'est qu'un guide pour les yeux) ([p-nitrophé nol] = 10 -4 mol•L -1 , [Au] = 5×10 -5 mol•L -1 , [NaBH4] = 3×10 -3 mol•L -1 ), [(co)polymè re] = 5 × 10 -3 % en poids.

III. 1

 1 Synthè se de P(BA-co-NIPAM) Trois familles de copolymè res de P(BA-stat-NIPAM), PBA-b-PNIPAM et PNIPAM-b-PBA-b-PNIPAM ont é té synthé tisé es par polymé risation par transfert de chaî ne par additionfragmentation ré versible (RAFT)/conception macromolé culaire par é change de xanthates (MADIX) polymé risation. Pour chacun d'eux, une valeur Mn similaire de 10 000 g•mol -1 (en abré gé 10k) a é té sé lectionné e, les structures des copolymè res dibloc, tribloc et statistiques sont donné es dans le Sché ma III.1. Leurs proprié té s ont é té caracté risé es par des mesures RMN, SEC et DSC. Sché ma III.1. Structures de P(BA-co-NIPAM) utilisé es dans ce chapitre. III.2 Dé termination de Tc en solution dilué e Pour é valuer l'influence de la composition et de la microstructure sur la Tc, le comportement des solutions de polymè res a é té é tudié en fonction de la tempé rature par mesure xii xii Ré sumé de thè se DSC (Figure III.1). Par rapport à l'homopolymè re PNIPAM, l'incorporation d'un monomè re hydrophobe dans la chaî ne PNIPAM a conduit à une diminution significative de Tc quelle que soit la structure considé ré e. En plus de cet effet de composition, l'effet de la microstructure est trè s prononcé . Ainsi, pour une composition donné e (c'est-à -dire 80 % en poids de PNIPAM), la Tc mesuré e pour un copolymè re statistique est bien infé rieure à celle mesuré e pour les structures tribloc et dibloc. Dans le cas d'un copolymè re statistique, sa microstructure spé cifique semble dé savantager fortement l'hydratation du polymè re. Elle ne permet pas non plus d'é tudier des copolymè res contenant des fractions de PBA supé rieures à 20 % en poids. Enfin, les valeurs lé gè rement infé rieures de Tc pour les structures triblocs par rapport aux diblocs pourraient ê tre lié es à un phé nomè ne similaire : en effet, pour une composition donné e, les structures triblocs pré sentent une transition supplé mentaire entre les blocs PBA et PNIPAM. En plus des effets sur la Tc, la microstructure impacte é galement fortement la solubilité des diffé rents polymè res é tudié s. Ainsi, les copolymè res à structure statistique pré sentent une faible solubilité dans les solutions aqueuses, tandis que les copolymè res diblocs et triblocs grâ ce à leur structure amphiphile spé cifique permettent d'obtenir des solutions limpides pour des rapports pondé raux allant jusqu'à 20 % en poids.

Figure III. 1 .III. 3

 13 Figure III.1. Tempé ratures de point de trouble Tc obtenues par DSC par chauffage (traits rouges pleins) ou refroidissement (traits bleus ouverts) pour l'homopolymè re PNIPAM et les copolymè res statistiques, diblocs et triblocs à base de PNIPAM à une concentration de 1% en poids.III.3 Comportement d'auto-assemblage du P(BA-co-NIPAM) en solution dilué e

Figure III. 2 .Figure III. 3 .

 23 Figure III.2. Images MET de PNIPAM4k-b-PBA2k-b-PNIPAM4k (A) à 20 o C et (B) à 36 o C. Intensité de diffusion en unité s absolues (cm -1 ) de D2O de PNIPAM4k-b-PBA2k-b-PNIPAM4k (+) et PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k (o) (C) à 20 o C et (D) à 36 o C.III.4 Thermoré activité du P(BA-co-NIPAM) en solution concentré e

Figure III. 4 .IV. 1 IV. 2

 412 Figure III.4. Images cryo-SEM de structures de gel à 40 o C obtenues à partir de (A) PNIPAM4k-b-PBA2k-b-PNIPAM4k et (B) PBA2k-b-PNIPAM8k. En ré sumé , la microstructure du P(BA-co-NIPAM) module significativement les proprié té s d'auto-assemblage, morphologiques et mé caniques de ces maté riaux en milieu aqueux. À composition similaire, le BA hydrophobe dans les copolymè res à blocs contribue à une diminution de Tc par rapport au PNIPAM pur dans une bien moindre mesure par rapport aux structures statistiques. De plus, les structures à blocs infé rieures à Tc de composition approprié e conduisent à la formation d'agré gats colloï daux. Au-dessus de Tc, la formation d'agré gats colloï daux est observé e à de faibles concentrations et des gels se forment à des concentrations plus é levé es. Pour une composition donné e, les copolymè res diblocs conduisent à des structures plus grosses et plus denses par rapport aux analogues triblocs et permettent la

Figure IV. 1 .

 1 Figure IV.1. Changement de transmittance de PN5k-b-PD5k, PN5k et PD5k à pH 10 ([(co)polymè re] = 1 % en poids). Pour mieux comprendre le mé canisme à l'origine de cette transition, une analyse par RMN 1H a é té ré alisé e avec une augmentation de tempé rature de 20 à 50 °C (Figure IV.2A). Les deux inté grales des unité s PN et PD sont resté es à peu prè s constantes jusqu'à 32 °C, ce qui est suivi d'une tendance à la baisse en fonction de la tempé rature, confirmant en outre le fait qu'avec l'augmentation de la tempé rature, les blocs PN et PD subissent des transitions de soluble à insoluble. dans cette gamme de tempé rature qui va induire la formation de gros agré gats.

Figure IV. 2 .

 2 Figure IV.2. Images MET, cryo-TEM et distribution de taille moyenne en nombre de PN5k-b-PD5k (A) (C) (E) à 25 o C et (B) (D) (F) à 60 o C (pH = 10, é chantillons TEM ont é té coloré es avec une solution d'acé tate d'uranyle à 2 % en poids). À 25 o C, en raison de la proprié té amphiphile (groupe hydrophobe -C12H25 et chaî nes hydrophiles PN, PD), des micelles sphé riques avec noyau -C12H25 et couronne PN, PD sont observé es. À 60 o C, les chaî nes PN et PD s'effondrent sont dé shydraté es et deviennent hydrophobes, les structures micellaires observé es à 25 o C ont tendance à s'agré ger, ce qui a entraî né la formation d'objets sphé riques plus gros. À travers les morphologies et la taille des agré gats de PN5k-b-PD5k formé s à une tempé rature infé rieure et supé rieure à Tc à pH 10, la transition morphologique induite par la tempé rature est repré senté e dans le Sché ma IV.3.

Figure IV. 3 .V. 1

 31 Figure IV.3. Changement de transmittance de PN5k-b-PD5k, PN5k et PD5k à pH 4 en fonction de la tempé rature ([(co)polymè re] = 1 % en poids, vitesse de chauffage = 1 o C•min -1 ). Le mé canisme derriè re ces transitions a é té analysé par des spectres RMN 1 H avec une augmentation de tempé rature de 20 à 50 °C. Avec l'augmentation de la tempé rature, seul le bloc PN subit une transition de soluble à insoluble. Alors que les inté grales des unité s PD n'ont pas de changement significatif dans la plage de tempé rature é tudié e. La structure colloï dale obtenue à partir d'une solution aqueuse de PN5k-b-PD5k a é té é tudié e par MET, cryo-TEM et DLS à 25, 30 et 60 °C (voir Figure IV.4).

Figure V. 1 .V. 2

 12 Figure V.1. Graphiques de (A) transmittance et (B) taille des agré gats en fonction de la tempé rature pour la solution aqueuse de PD5k avant, aprè s bullage de CO2 et aprè s bullage de N2 ([PD5k] = 1 % en poids).V.2 Ré activité thermique et au CO2 des copolymè res sé quencé s PN5k-b-PD5k

Figure V. 2 .

 2 Figure V.2. Changement de transmittance de la solution PN5k-b-PD5k en fonction de la tempé rature avant, aprè s bullage avec CO2 et aprè s bullage avec N2. ([PN5k-b-PD5k] = 1 % en poids)

Figure V. 3 .

 3 Figure V.3. Images MET (A) avant, (B) aprè s traitement au CO2, (C) aprè s exposition à N2 et (D) Taille hydrodynamique distribué e en nombre de PN5k-b-PD5k à 25 o C ([PN5k-b-PD5k] = 0,1 % en poids, é chantillons coloré s avec une solution d'acé tate d'uranyle à 2 % en poids).(ii) À une tempé rature supé rieure à Tc

Figure V. 4 .

 4 Figure V.4. Images MET des agré gats PN5k-b-PD5k (A) avant, (B) aprè s exposition au CO2 et (C) aprè s exposition au N2 à 60 o C ([PN5k-b-PD5k] = 0.1 % en poids, é chantillons coloré avec une solution d'acé tate d'uranyle à 2 % en poids). Comme l'ont ré vé lé les analyses MET et DLS, PN5k-b-PD5k s'est auto-assemblé en structures sphé riques de diffé rentes tailles dans toutes les conditions é tudié es. Une illustration sché matique de PN5k-b-PD5k sous des stimuli de tempé rature et de CO2 est proposé e dans le Sché ma V.2.

Table I .

 I

3 Tc shifted by incorporation of hydrophilic/hydrophobic comonomers.

Table I . 4

 I4 Thermoresponsive (co)polymers with LCST-LCST behavior in water.

	Copolymer	Tc,1 ( o C) a	Tc,2 ( o C) a	Ref.
	PNIPAM137-b-PEAM67	17	62
				[140]
	PNIPAM34-b-PEAM94	27	58
	PEOVE300-b-PMOVE300	20	50	[128]
	PNASME170-b-PNIPAM63	38	43	[12]
	PDMAEMA51-b-PDEGMA49	34.4	46.1	[141]

Table I .5 Thermoresponsive (co)polymers with LCST-UCST behavior.

 I

	40 Chapter I. Literature Review
	Copolymer	Solvent	Tc ( o C) a	TCL ( o C) a	Ref.
	Tc < TCL
		Acidic water
	P(A-Pro-OMe)27-b-P(A-Hyp-OH)73	(containing	20	40	[156]
		NaCl)
	PNIPAM94-b-P(NAG19-co-NAGSP30)	H2O	42.5	63	[157]
	P(SPB0.51-co-Bz0.23-co-THF0.26)	H2O	37.9	67.8	[158]
	P(amido thioether) (containing N-
	diethylaminoethylamido and N-	H2O (pH=8.14)	36.4	66.3	[159]
	hydroxyethylamido)
	PEO45-b-P(AAm-stat-AN)	H2O	30	50	[160]
		40

Table I .5 (Continued)

 I

	Copolymer	Solvent	Tc ( o C) a	TCL ( o C) a	Ref.
	Tc > TCL
	PtBMA329-b-PVEA142	methanol	53	32	[37]
	PBA5k-b-PNIPAM5k	[C2mim][NTf2]	53	16	[161]
	PDMAEMA-b-PSBMA	H2O (pH=9.0)	55	41	[162]
	PNIPAM95-b-PSPP33	H2O	33.4	8.6	[163]
	PdMMAEAPS-b-PDEAM	D2O	31	22	[69]
	PSB430-b-PNIPAM200	D2O	32.3 ± 0.5	21.2 ± 0.5	[164]
	P(AAm231-co-AN78)-b-PDMAEMA319	PBS	45.86	20.9	[165]
	P(DEGMA60-stat-OEGMA40)27-b-PMAAm440	H2O	66	56	[166]
	P(OEGMA-co-DEGMA)-b-P(MPS-co-DMAPMA)	H2O	61	21	[167]

Table I .7

 I Morphological transition of thermoresponsive diblock copolymer in dilute solution.

Table I .10 Self

 I -assembly of LCST-UCST typed copolymers in different temperature regions. Morphological transition & Examples a

Table I .11 Chemical

 I

structures and pKa values of pH-responsive homopolymers.

in Table I.13. Table I.13 Examples for

			block have been extensively studied. The study of organization properties
	in aqueous solution of such thermo-and pH-responsive copolymers is complex. In
	general, pH adjustment alters ionization/deionization (or protonation/deprotonation)
	state	of	pH-sensitive	segments,	while	temperature	change	shifts
	hydrophilic/hydrophobic balance of thermoresponsive moieties. Both changes
	influence the morphology of copolymers. Some examples of dual thermo-and pH-
	responsive diblock copolymers are listed

pH-and temperature-controlled morphological transition.

Table I .

 I

14 Morphological transition of CO2-responsive (co)polymers. Morphological transition triggered by CO2 & Examples

Table I .

 I 17 Synthesis of stimuli-responsive (co)polymers by RAFT polymerization.

			Experimental conditions a
	(Co)polymer	Stimulus type	Initial RAFT agent	Initiator	Ref.
	PDMAEEOMA137-b-PEMAEEOMA78	Dual temperature (LCST-LCST)	CDTPA	AIBN	[18]
	P(DEGA-stat-DMAm)	Temperature	DMP	AIBN	[23]
	PNIPAM94-b-P(NAG19-co-NAGSP30)	Dual temperature (LCST-UCST)	CDTPA	AIBN	[157]

Table II

 II

			Composition			DSC (solution 2%)
	Entry	Theoretical copolymer structure	VCL/VP weight ratio a	VCL/VP molar ratio a	Mn (g•mol -1 ) THF(DMF)	Dispersity (Ð) THF(DMF)	Tc ( o C) b ΔH (J•g -1 of VCL) c
	1	PVCL	100/00	100/00	14350	1.09	36.7	-30
	2	P(VCL75-stat-VP25)	75/25	70/30	16000 (13850)	1.04 (1.12)	50.8	-8
	3	P(VCL60-stat-VP40)	63/37	58/42	17000 (18500)	1.04 (1.19)	62.0	-3
	4	P(VCL50-stat-VP50)	51/49	45/55	(18400)	(1.07)	/ d	/ d
	5	P(VCL25-stat-VP75)	26/74	22/78	(19000)	(1.13)	/ d	/ d
	6	P(VCL10-stat-VP90)	10/90	8/92	(23200)	(1.12)	/ d	/ d
	7	PVP	0/100	0/100	(22000)		/ d	/ d

.

1

Copolymer composition and main characteristics of the synthesized (co)polymers.

a Determined by 1 H NMR spectra. b Evaluated by extrapolation to 0 °C•min -1 of the maximum of observed peak upon heating processes with different heating rates, standard deviation on Tc = ± 0.2 J•g -1 . c Obtained with a heating

1.00 2.94 A B rate

  of 2.5 °C•min-1 , standard deviation on ∆H = ± 2 J•g -1 . d No transition detectable. ( 1 H NMR and DSC measurements were done by X. Zhao in IMRCP, Toulouse, France)The cloud point temperature increases non-linearly from 36.7 to 50.8 and 62.0 °C for P(VCL-stat-VP)20k with VP content changing from 0 to 25 and 40% respectively (Entry 1-3 in TableII.1), which results from the introduction of the hydrophilic VP units. No transition occurs as VP content is higher than 40%. Further insight on the effect of VP introduction within PVCL chain is obtained through the measurement of associated variation of enthalpy (∆H) normalized with respect to VCL content. When VP fraction in copolymer increases, a strong decrease of ∆H is measured (TableII.1). This variation is clearly not proportional to VCL content, which is ascribed to a mechanism of dehydration involving the whole macromolecule structure, and not short sequences of VCL units. Indeed, insertion of VP units within the PVCL

backbone strongly impedes dehydration phenomenon by preventing release of water molecules from the polymer chains and therefore the formation of hydrophobic regions is responsible for the aggregation process and the formation of mesoglobules.

[27]

Consequently, only copolymers with low VP content (below 40%) present thermoresponsive behaviors in solution.

  Introduction ................................................................................................................. III.2.1 Synthesis of P(BA-co-NIPAM) copolymers ....................................................... III.2.2 Characterization of copolymers ........................................................................... III.4.1 Phase behavior in water at low temperature (T < Tc) .......................................... III.4.2 Self-assembly in water at high temperature (T > Tc) ...........................................

Nagasamy, B. Himangshu, K. Anuttam, Biomed J Sci Tech Res 4 (2018) 3765-3775. Contents III.1 III.2 Synthesis and characterization of copolymers .......................................................... III.3 Determination of cloud point temperatures of copolymer solutions ...................... III.4 Properties of block copolymer in dilute aqueous solution ....................................... III.5 Formation and characterization of thermosensitive hydrogels ............................... III.6 Thermoresponsiveness of copolymers at different conditions ................................. III.7 Conclusions ................................................................................................................... III.8 References .....................................................................................................................

Table III .

 III SEC analyses performed in THF with RI-MALS detection. b SEC analyses performed in DMF and calibrated with PMMA standards. The chosen conditions led to an overestimate of given mass by a factor of two.

	0.5k/9.5k	P(BA0.5k-stat-NIPAM9.5k)	10620 a	1.30 a	111.90	0.74
	1k/9k	P(BA1k-stat-NIPAM9k)	11230 a	1.57 a	114.20	0.71
		PBA2k-b-PNIPAM8k	10000 a	1.16 a	108.90	0.20
	2k/8k	P(BA2k-stat-NIPAM8k)	9100 a	1.81 a	100.40	0.63
		PNIPAM4k-b-PBA2k-b-PNIPAM4k	8960 a	1.40 a	100.60	0.28
		PBA5k-b-PNIPAM5k	9400 a	1.25 a	-48.00 106.70	0.10 0.20
	5k/5k
		PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k	11000 a	1.23 a	-35.20 86.21	0.10 0.28
	8k/2k	PBA8k-b-PNIPAM2k	10100 a	1.20 a	-44.00 133.00	0.40 0.10
		PNIPAM1k-b-PBA8k-b-PNIPAM1k	9900 a	1.36 a	-41.70	0.56
		PBA2k	2400 a	1.38 a	-50.70	0.50
	PBA	PBA5k	5750 a	1.35 a	-50.60	0.50
		PBA8k	9500 a	1.30 a	-50.70	0.50
		PNIPAM8k	17600 b	1.27 b	127.90	0.40
	PNIPAM	PNIPAM10k	21300 b	1.31 b	126.20	0.46

1 Characteristics of various copolymers prepared by RAFT/MADIX polymerization: Mn, Ð and glass transition temperatures (Tg).

PBA /PNIPAM Sample Mn (g• mol -1 ) Ð T g c (º C) ΔC p c

(J• g -1 • K -1 )

a c Glass transitions measured by DSC technique with a heating rate of 10 °Cmin -1 .

Table III . 2

 III2 Cloud points of copolymer aqueous solutions obtained by visual assessment, DSC, DLS and turbidimetry measurements. DSC, DLS and turbidimetry measurements were 1, 1, 0.1 and 0.1 wt.%, respectively. ΔH values calculated per gram of PNIPAM present in the considered copolymers.)

							DSC			DLS	Turbidimetry
	PNIPAM weight	(Co)polymer	Visual assessment	heating	Cooling	heating heating cooling
	fraction				Tc(º C)	Tc	ΔH	Tc	ΔH	Tc	Tc	Tc
	(%)					(º C) a	(J•g -1 )	(º C) a	(J•g -1 )	(º C)	(º C) b	(º C) b
	100	PNIPAM10k	30	37.67 -14.00 36.16 18.00	37.00	35.28	35.02
	95	P(BA0.5k-stat-PNIPAM9.5k)	19	23.15 -29.47 21.24 31.58	21.00	24.40	22.60
	90	P(BA1k-stat-NIPAM9k)	insoluble	17.75 -18.89 15.45 13.33	17.00	21.49	17.28
		PBA2k-b-PNIPAM8k	32	28.80 -13.75 27.60 13.75	27.00	29.42	26.48
	80	P(BA2k-s-NIPAM8k) PNIPAM 4k -b-	insoluble	/ c	/ c	9.62	2.25	/ c	/ c	/ c
		PBA	2k -b-	25	26.00 -18.75 25.13 15.00	26.00	27.70	25.50
		PNIPAM	4k
		PBA5k-b-PNIPAM5k	28	27.35 -13.20 26.44 10.60	24.00	28.73	26.69
	50	PNIPAM2.5k-b-
		PBA5k-b-	20	/ c	/ c	21.74	8.00	24.00	22.45	18.33
		PNIPAM2.5k

a Determined by extrapolation to 0 o C• min -1 of peak values on the thermogram upon heating/cooling at different rates. b Determined by extrapolation to 0 o C• min -1 of inflection points of transmittance curves at different heating/cooling rates. c Not determined. (Copolymer concentrations used for visual assessment,

Synthesis and characterization of homo-and copolymers

  whose intermediate microstructures between block and statistical should enable to further modulate thermoresponsiveness of polymers and to obtain micellar aggregates with improved dynamics of assembly. Introduction .............................................................................................................. ...................................

	Contents
	IV.1 IV.2 IV.3

Thermoresponsive behavior of homopolymer solutions

  ....................................... IV.3.1 PN homopolymer ................................................................................................. IV.3.2 PD homopolymer .................................................................................................

	IV.4

Thermoresponsive properties of PN-b-PD in water

  .............................................. IV.4.1 Thermoresponsive behavior of PN5k-b-PD5k solution at pH 10 .......................... IV.4.2 Thermoresponsive behavior of PN5k-b-PD5k solution at pH 4 ............................ IV.4.3 Effect of pH on thermoresponsive property of PN5k-b-PD5k solution .................

IV.4.4 Effect of copolymer composition on thermoresponsive properties ..................... IV.5 Conclusions ............................................................................................................... IV.6 References .................................................................................................................

Table IV .

 IV 5 PN-b-PD aggregates size at different temperatures and pH values determined by TEM and DLS measurements.

			Condition	Aggregate size (d. nm)
	Technique	pH	Temperature ( o C)	PN2k-b-PD8k	PN5k-b-PD5k	PN8k-b-PD2k
		10	25 60	27.9 ± 6.5 19.9 ± 3.3	23.2 ± 5.7 92.8 ± 34.6	21.7 ± 5.0 56.3 ± 16.0
	TEM	4	25 30 40	18.3 ± 2.7 / a 21.9 ± 4.1	23.1 ± 5.2 30.4 ± 8.9 / a	20.5 ± 4.1 / a / a
			60	30.3 ± 5.9	125.6 ± 38.8	201.0 ± 51.7
			25	45.9 ± 3.4	27.0 ± 8.8	4.1 ± 1.3
		10
			60	109.4 ± 1.9	188.5 ± 3.1	137.8 ± 3.9
			25	30.7 ± 22.5	25.8 ± 9.4	31.1 ± 4.2
	DLS		30	/ a	77.4 ± 8.5	/ a
		4	40	64.4 ± 55.0	/ a	/ a
			60	154.0 ± 3.2	200.3 ± 4.5	321.8 ± 2.7

a Not detected. ([PN-b-PD] = 0.1 wt.%, TEM samples stained with 2 wt.% uranyl acetate solution)

Table V .

 V 2 PN-b-PD aggregates size upon CO2 treatment/removal at 25 and 60 o C determined by TEM and DLS measurements.

				Aggregates size (d. nm)
	Technique	Condition
			PN2k-b-PD8k	PN5k-b-PD5k	PN8k-b-PD2k
		Initial	27.9 ± 6.5	23.2 ± 5.7	21.7 ± 5.0
	25 o C	After bubbling CO2	33.6 ± 11.1	28.7 ± 7.8	36.6 ± 8.2
		After bubbling N2	22.3 ± 4.2	23.0 ± 5.0	18.0 ± 4.2
	TEM
		Initial	19.9 ± 3.3	92.8 ± 34.6	56.3 ± 16.0
	60 o C	After bubbling CO2	19.5 ± 4.9	35.1 ± 7.4	54.3 ± 14.0
		After bubbling N2	24.6 ± 5.4	61.6 ± 13.5	27.8 ± 5.0
		Initial	45.9 ± 3.4	27.0 ± 8.8	4.1 ± 1.3
	25 o C	After bubbling CO2	46.3 ± 26.9	68.9 ± 23.9	45.0 ± 13.0
		After bubbling N2	34.3 ± 8.2	51.3 ± 7.6	/ a
	DLS
		Initial	109.4 ± 1.9	188.5 ± 3.1	137.8 ± 3.9
	60 o C	After bubbling CO2	119.3 ± 3.6	174.6 ± 4.5	209.0 ± 5.4
		After N2	160.5 ± 5.6	166.3 ± 4.9	/ a
	a Not determined. (Gas flow rate was 10 mL• min -1 , 10 and 30 min for bubbling CO2 and N2 respectively.)

Table ES . 1

 ES1 Step 1: Synthesis of PBAxk block.

	Homopolymer	AIBN (g/mmol)	Bis-xanthate X2 (g/mmol)	Ethanol (g/mmol)	BA (g/mmol)	Conv./%
	PBA2k	0.01037 (0.0632)	0.22493 (0.4998)	0.6982 (15.16)	1.06 (8.263)	99
	PBA5k	0.00922 (0.0561)	0.19974 (0.452)	0.61994 (13.46)	2.2590 (17.625)	98
	PBA8k	0.01024 (0.0624)	0.22115 (0.4996)	0.68294 (14.82)	4.019 (31.24)	98

Table ES . 2

 ES2 Step 2: Synthesis of triblock copolymers.

	Triblock copolymer	AIBN (g/mmol)	Synthesized PBA (g/mmol)	Ethanol (g/mmol)	NIPAM (g/mmol)	Conv. /%	[NIPAM] : [BA]
	PNIPAM 4k -b-PBA 2k -b-PNIPAM 4k	0.0399 (0.243)	0.8428 (0.4214)	2.907 (64.66)	2.800 (24.74)	98	4.37
	PNIPAM 2.5k -b-PBA 5k -b-PNIPAM 2.5k	0.03209 (0.1954)	2.40907 (0.482)	2.2184 (48.123)	2.2192 (19.609)	100	1.21

Table ES . 3

 ES3 Synthesis of statistical copolymers (see Scheme ES.5). Synthesis of DEAEAM.

		In the case of PD5k (see Scheme ES.9), a mixture of DEAEAM (2 g, 11.747 mmol), AIBN ES.3 Characterization
		(0.050 g, 0.305 mmol), CDTPA (0.176 g, 0.435 mmol), 1,3,5-trioxane (0.106 g, 1.175 mmol,
		as internal standard) and 1,4-dioxane (3.497 g) was placed into a Schlenk flask with a magnetic ES.3.1 NMR spectroscopy
		stir, the flask was degassed by three freeze-pump-thaw cycles and placed in a preheated oil bath 1 H and 13 C NMR spectra were recorded on Bruker ARX 400 at 400.13 MHz (or Bruker
		at 70 °C. After a given time, the polymerization was quenched by rapid immersion of flask in ARX 500 at 500.13 MHz) and at 100.61 MHz, respectively. All spectra were referenced to the
		liquid nitrogen. PD5k was purified by dialysis against deionized water for three days and dried solvent residual peak.
		by lyophilization (conversion: 95.4%). Mn,theo = 4790 g• mol -1 . Mn,NMR = 4810 g• mol -1 , which is
		calculated by comparing integrals of signal at 0.88 ppm (RAFT terminal, -CH3) to signal at 3.33 ES.3.2 Size Exclusion Chromatography (SEC)
		ppm (DEAEAM, -CH2-adjacent to -CONH-group) in 1 H NMR spectrum. In DMF (containing Number-average molecular weights (Mn ) and dispersities (Ð) of all synthesized
		10 mM LiBr): Mn,SEC = 6900 g• mol -1 , Ð = 1.21; in THF (containing 2 v% TEA): Mn,SEC = 4210 homopolymers and copolymers in Chapters II, III and IV were determined by SEC on an
		g• mol -1 , Ð = 1.09. 1 H NMR (500 MHz, D2O, 25 o C) δH (ppm): 3.33 (s, 2H, -CONH-CH2-), apparatus equipped with a Varian ProStar 325 UV detector (dual wavelength analysis) and a
		2.64 (s, 6H, -N(CH2)3), 2.31-1.62 (m, -CH2CH-CONH-, -CH2CH-CONH-, -C(CN)-CH3)-, Waters 410 refractive index detector as well as two Shodex K-805L columns (8 mm×300 mm,
		-CH2CH2COOH, -CH2CH2COOH), 1.26 (s, 20H, -(CH2)10-CH3), 1.08 (s, 6H, -N(CH2CH3)2), 13 µm). Molecular weights were calculated based on RI-MALS detection. [4] The value of
		0.88 (t, 3H, -(CH2)10-CH3). dn/dc for block or statistical copolymers were calculated by using the measured values of
		Other PN, PD homopolymers and block copolymers of PN-b-PD with variable homopolymer weighted by the composition of measured copolymer. Typically, (co)polymer
		compositions were synthesized with the similar procedure. The detailed information is samples were prepared with a concentration of 10 mg• mL -1 and filtered through 0.45 µm PTFE
	Statistical copolymer summarized in Table ES.4. AIBN (g/mmol) filter. The eluents used in chapter II was DMF containing 10 mM LiBr, in Chapter III was xanthate X1 (g/mmol) BA (g/mmol) 1,4-NIPAM Con. [NIPAM] : dioxane (g) (g/mmol) /% [BA] Table ES.4 Synthesis of PN, PD homopolymers and block copolymers of PN-b-PD. THF, and in Chapter IV were DMF containing 10 mM LiBr and THF containing 2 v% TEA,
	P(BA2k-stat-NIPAM8k) P(BA1k-stat-NIPAM9k) 2 (17.674) (Co)polymer NIPAM PN8k (g/mmol) DEAEAM 0.055 (0.338) 0.028 (0.169) 0 0.106 (0.263) (g/mmol) CTA (g/mmol) (0.511) 0.106 0.0532 (0.0255) (0.132) 0.022 AIBN (g/mmol) the flow rate was set at 1 mL•min -1 . PN2k 2 (17.674) 0 0.506 (1.253) (0.626) 0.103 ES.3.3 Differential Scanning Calorimetry (DSC) (7.802) 1.00 0.25 (1.951) [M]0 :[CTA]0 :[AIBN]0 5.162 (35.348) 4.00 2.581 (19.883) 67 : 1 : 0.5 4.256 2.25 1,4-Dioxane (g) 14 : 1 : 0.5 5.217	99 99 Temperature 4.20 75 8.65 (°C) 75	0 Trioxane (g/mmol) 0
	P(BA0.5k-stat-NIPAM9.5k) PN10k 2 (17.674)	0	0.0277 (0.169) 0.084 (0.208)	0.0532 (0.0255) 0.017 (0.104)	0.125 (0.975)	2.581 85 : 1 : 0.5	2.375 (20.988) 4.202	99	75	11.33	0
	ES.2.3 Methods of synthesis used in Chapter IV PN2k-b-PD8k 0 2 (11.747) 0.484 (0.248) 0.037 (0.224)	47 : 1 : 0.9	5.254		70	0.106 (1.175)
	(i) Synthesis of monomer of N,N-(diethylamino) ethyl acrylamide (DEAEAM) PN8k-b-PD2k 0 0.2 (1.175) 1.592 (0.179) 0.026 (0.161) 6.6 : 1 : 0.9 3.658		70	0.011 (0.117)
	PD2k	0	2 (11.747)	0.506 (1.253)	0.144 (0.877)		9 : 1 : 0.7	4.133		70	0.106 (1.175)
	PD8k	0	2 (11.747)	0.106 (0.263)	0.030 (0.184)		45 : 1 : 0.7	3.363		70	0.106 (1.175)
	PD10k	0	2 (11.747)	0.084 (0.208)	0.024 (0.146)		56 : 1 : 0.7	3.321		70	0.106 (1.175)

Scheme ES.

6

1 (co)polymè res thermosensibles Les

  IntroductionLes (co)polymè res sensibles aux stimuli ou dits « intelligents » ont sé duit ces derniè res anné es en raison de l'alté ration de leurs proprié té s physico-chimiques (solubilité , conformation de la chaî ne, proprié té s d'agré gation, etc.) pour s'adapter aux changements de l'environnement exté rieur. Cette ré activité rapide et ré versible confè re à ces (co)polymè res de multiples applications potentielles (telles que l'administration et la libé ration contrôlé e de mé dicaments, les capteurs, les textiles intelligents et les membranes fonctionnalisé es, etc.).Le mé canisme de ré ponse est attribué à la modification des interactions inter-ou intramolé culaires induites par une ré ponse au stimulus. De plus, le niveau de ré ponse dé pend fortement des conditions externes (telles que la nature du stimulus et son intensité , les solvants choisis, la pré sence d'additifs, etc.) et des paramè tres structuraux du (co)polymè re (tels que (co)polymè res thermosensibles subissent gé né ralement un changement de solubilité dans l'eau en ré ponse à une modification de tempé rature. Un bel é quilibre hydrophobehydrophile dans leur structure est responsable de ce phé nomè ne. De petits changements de tempé rature autour d'une valeur critique induisent l'effondrement ou l'expansion des chaî nes polymè res en ré ponse aux nouveaux ajustements des interactions hydrophobes et hydrophiles entre le polymè re et l'eau. La tempé rature à laquelle se produit la sé paration des phases est appelé e tempé rature de point de trouble (Tc).

	Concernant la difficulté de synthé tiser des copolymè res thermosensibles multiples bien
	dé finis, la combinaison de deux blocs thermosensibles ou plus est une straté gie courante pour
	obtenir des maté riaux avec une transition de phase par é tapes ou un comportement d'auto-
	assemblage. Sur la base du type thermosensible et de la tempé rature de transition de phase, les
	copolymè res thermosensibles doubles sont classé s en types LCST-LCST, LCST-UCST et
	UCST-UCST.
	Changement de solubilité induit par la tempé rature des fractions thermosensibles, qui
	influence davantage la formation/modification des agré gats en solution. Les morphologies de
	ces agré gats et l'effet de la tempé rature sur la structure des agré gats peuvent ê tre é tudié s par
	Selon le comportement de transition de phase, il existe principalement deux caté gories de diffusion (lumiè re, neutrons et rayons X) ou par des mesures de microscopie. Les (co)polymè res

l'architecture (bloc, statistique), composition, concentration en (co)polymè res, poids molé culaire et dispersité ).

Chapitre I

Dans le Chapitre I, les principales familles de (co)polymè res sensibles aux stimuli (thermo, pH et CO2) sont passé es en revue, leurs proprié té s de ré ponse correspondantes (comportement de transition de phase et comportement d'auto-organisation) lors de l'application/suppression des stimuli, impacts pour affectant la ré activité , les principales straté gies de polymé risation et leurs applications sont pré senté es avec une description dé taillé e.

I.

(co)polymè res thermosensibles, leurs diagrammes de phases sont pré senté s dans le Sché ma I.1.

La premiè

re famille est constitué e de (co)polymè res avec une tempé rature de solution critique infé rieure (LCST), cette famille subit une transition de phase d'une ré gion monophasique à une iv Ré sumé de thè se ré gion biphasique lors du chauffage. La deuxiè me famille est celle des (co)polymè res à tempé rature critique supé rieure de solution (UCST), ce type de (co)polymè res pré sente un comportement opposé : une transition d'une ré gion biphasique à une ré gion monophasique est gé né ralement observé e lors du processus de chauffage. Sché ma I.1. Diagrammes de phases de (co)polymè res thermosensibles avec un comportement (A) LCST et un comportement (B) UCST. Tc fait ré fé rence à la tempé rature à laquelle une transition de phase de (co)polymè res thermosensibles à une concentration fixe a lieu. Sa dé termination est un pré alable aux applications potentielles. Diffé rentes techniques, notamment la turbidimé trie, la diffusion dynamique de la lumiè re (DLS), la calorimé trie diffé rentielle à balayage (DSC), la spectroscopie par ré sonance magné tique nuclé aire (RMN) et la spectroscopie infrarouge à transformé e de Fourier (FTIR) ont é té adopté es dans la litté rature. Le ré glage fin de Tc est un point clé pour é largir les applications potentielles des polymè res thermosensibles, ce qui peut ê tre ré alisé en modifiant le poids molé culaire, la concentration en (co)polymè res, la structure topologique, la polarité des comonomè res incorporé s, les groupes terminaux, les additifs, etc. thermosensibles dans diffé rentes ré gions de concentration affichent divers é tats d'agré gation, tels que des unimè res, des nanoparticules à gé omé trie micellaire sphé rique, vermiforme et vé siculaire en solution dilué e ainsi que sol et hydrogel en solution concentré e. v Ré sumé de thè se v I.

2 (co)polymè res sensibles au pH L

  'é lé ment clé des polymè res sensibles au pH est la pré sence de fragments acides ou basiques faibles ionisables attaché s à un squelette hydrophobe. Lors de l'ionisation, les chaî nes enroulé es s'é tendent de faç on spectaculaire en ré ponse aux ré pulsions é lectrostatiques des anions ou des cations gé né ré s. Cependant, l'ionisation complè te sur les polyé lectrolytes est plus difficile en raison des effets é lectrostatiques exercé s par d'autres groupes ionisé s adjacents.Cette transition entre l'é tat é troitement enroulé et expansé est influencé e par toute condition qui modifie la ré pulsion é lectrostatique, telle que la force ionique et le type de contre-ions. Par consé quent, il faut garder à l'esprit qu'aprè s plusieurs cycles de protonation/dé protonation par addition d'acides ou de bases, l'accumulation de sel peut avoir un effet né faste sur l'organisation des (co)polymè res en solution.Selon les groupes fonctionnels, les polymè res sensibles au pH sont divisé s en deux caté gories : les polymè res avec des groupes acides et les polymè res avec des groupes basiques. hydrophobe à un pH spé cifique, les impacts de diffé rents paramè tres tels que le pH, la longueur de chaî ne sensible au pH, la concentration en sel, ( l'architecture des copolymè res sur la forme et la taille des agré gats doit ê tre prise en compte.Les (co)polymè res sensibles au CO2 sont des (co)polymè res susceptibles de ré agir avec le CO2 en solution aqueuse, cette ré action peut ê tre inversé e lors d'une aé ration alterné e CO2/gaz inerte. En tant que stimulus, le CO2 a des perspectives prometteuses en raison de son abondance, de son ininflammabilité , de sa faible toxicité et de sa biocompatibilité . De plus, le CO2 est facile à é liminer sans aucune accumulation ni contamination dans le systè me lors de cycles ré pé té s.La ré activité au CO2 des (co)polymè res est obtenue par l'incorporation de groupes fonctionnels sensibles au CO2 le long des chaî nes polymè res. Les groupes fonctionnels sensibles au CO2 les plus rapporté s sont les organobases telles que : amine, amidine, guanidine et imidazole.

	vi Ré sumé de thè se
	L'auto-assemblage de doubles (co)polymè res thermosensibles et sensibles au pH est
	relativement	complexe.	Gé né ralement,	l'ajustement	du	pH	modifie	l'é tat
	d'ionisation/dé ionisation (ou de protonation/dé protonation) des segments sensibles au pH,
	tandis que le changement de tempé rature modifie l'é quilibre hydrophilie/hydrophobie des
	fragments thermosensibles. Les deux changements influencent la morphologie des copolymè res.
	I.3 (co)polymè res sensibles au CO2
	La transition morphologique induite par le pH des (co)polymè res liné aires (tels que bloc,
	statistique, gradient, etc.) est l'objet le plus é tudié . À l'exception des transitions des unimè res
	vers les micelles dé clenché es par le pH, des micelles vers les micelles inverses et des vé sicules
	vers les vé sicules inverses, les vé sicules vers les cylindres vers les sphè res, les unimè res vers le
			vi

Les polyacides faibles sont non protoné s avec des charges né gatives à pH neutre et é levé . Les polybases faibles avaient un comportement opposé , é tant protoné es à de faibles valeurs de pH.

Pour ces (co)polymè res sensibles au pH, il est donc crucial de dé terminer la constante de dissociation acide, Ka (ou son log né gatif : pKa) pour savoir à quel pH se produit la transition ionique/non ionique. L'ajustement du pH modifie le degré de protonation/dé protonation des fractions sensibles au pH et la ré pulsion é lectrostatique parmi les chaî nes chargé es, ce qui influence le ré seau de liaison hydrogè ne, les interactions ioniques/hydrophobes dans le systè me, et provoque en outre un changement de solubilité des (co)polymè res en solution aqueuse . Bien comprendre et contrôler le comportement d'auto-assemblage des (co)polymè res sensibles au pH, en dehors du rapport hydrophile/mé lange de micelles et les amas de micelles, les sphè res vers -un mé lange de micelles et de vé sicules ressemblant à des vers, et des transitions sphè res-vé sicules sont é galement observé es dans la litté rature.

La solubilité en solution aqueuse de (co)polymè res est fortement influencé e par la protonation/dé protonation provoqué e par le traitement/l'é limination du CO2. En raison de la modification de l'é quilibre hydrophile/hydrophobe dans le systè me, les (co)polymè res peuvent s'assembler en diffé rents agré gats avec des gé omé tries, tailles variables... De plus, les impacts de l'architecture (co)polymè re, sé quence de blocs et (co)polymè re la composition doit é galement ê tre prise en compte lors de l'analyse de l'agré gation des particules.

I.

4 Mé thode synthé tique de (co)polymè res stimuli-sensibles La

  synthè se pré cise de (co)polymè res bien dé finis est une condition pré alable pour obtenir les proprié té s souhaité es, telles que le ré glage pré cis des valeurs de Tc sur une large plage de tempé ratures ou le contrôle de l'auto-assemblage dé clenché par des stimuli externes. Pour atteindre un tel objectif, les mé thodes de polymé risation radicalaire contrôlé es telles que la Ré sumé de thè se vii microstructure avancé e. Grâ ce à ces techniques sophistiqué es et à la modification postpolymé risation, un grand nombre de (co)polymè res ré actifs multi-stimuli ont é té synthé tisé s.

	polymé risation radicalaire induite par le nitroxyde (NMP), la polymé risation radicalaire par
	transfert d'atomes (ATRP), la polymé risation par transfert de chaî ne par addition-fragmentation
	ré versible (RAFT) sont les outils de choix. En effet, le dé veloppement rapide de la
	polymé risation radicalaire contrôlé e fournit des informations pour concevoir et synthé tiser des

(co)polymè res avec un poids molé culaire contrôlé , une polydispersité é troite et une vii I.

5 Applications des (co)polymè res sensibles aux stimuli

  En effet, le revê tement des AuNPs avec des stimuli sensibles est un moyen pratique de modifier de maniè re ré versible les proprié té s des AuNPs. Des polymè res thermosensibles au comportement de type LCST ont é té greffé s sur des AuNPs sans perdre leur thermoré activité .

	Les (co)polymè res ré actifs aux stimuli multiples sont un type de maté riaux intelligents et
	ont suscité un grand inté rê t ces derniè res anné es. En raison de leur changement de proprié té s
	physicochimiques (telles que la solubilité , la conformation de la chaî ne, la dimension, la
	configuration…) domaines de la biotechnologie, de la nanotechnologie, des membranes
	fonctionnelles et des revê tements intelligents.
	II.1 Synthè se de P(VCL-stat-VP)20k
	La synthè se d'homopolymè res (PVCL et PVP) et de copolymè res de VCL et VP a é té
	pré cé demment ré alisé e par X. Zhao dans notre laboratoire. Il s'agit d'une sé rie de copolymè res

Chapitre II

Les nanoparticules mé talliques, en particulier les nanoparticules d'or (AuNPs), ont attiré beaucoup d'attention en raison de leurs proprié té s é lectroniques, optiques et catalytiques uniques ré sultant de leur large application allant de l'optoé lectronique à la biologie. Ces proprié té s dé pendent fortement de la taille et de la forme des particules, de la nature de l'enveloppe organique protectrice et de la distance interparticulaire. Les AuNP sont instables du point de vue colloï dal et sont susceptibles d'agré gation irré versible, mais elles peuvent ê tre stabilisé es par greffage ou adsorption de petites molé cules organiques telles que des citrates, des tensioactifs, des ligands ou des polymè res. Ces molé cules organiques constituent un outil supplé mentaire pour moduler les proprié té s physico-chimiques. À cette fin, les polymè res se sont avé ré s ê tre un maté riau de choix en raison de leur flexibilité pour des utilisations spé cifiques sur mesure et é galement pour leurs proprié té s de stabilisation à long terme supé rieures à celles des petites molé cules. Des exemples notables incluent les polymè res ré actifs. statistiques de VCL et VP de Mn prédéterminé (20000 g•mol -1 ) et de compositions diverses qui ont é té synthé tisé s par polymé risation RAFT/MADIX (Sché ma II.1), leurs proprié té s en solution aqueuse ont é té dé terminé es par nuclé aire spectroscopie par ré sonance magné tique viii viii Ré sumé de thè se

  Les Figures II.1B pré sentent les ajustements des donné es expé rimentales obtenues à diffé rentes tempé ratures pour Au@P(VCL75-stat-VP25). Dans un premier temps, il existe une pé riode d'induction qui est lié e à une restructuration de surface des nanoparticules avant le dé marrage de la ré action catalytique. La ré action ne peut se produire qu'entre espè ces adsorbé es en surface. L'é volution de la constante ciné tique de pseudo-premier ordre (kobs) en fonction de la tempé rature pour Au@P(VCL75-stat-VP25) a é té donné e sur la Figure II.1C. Les ré sultats suggè rent que l'activité catalytique augmente avec la tempé rature jusqu'à ce que le point de trouble soit atteint, aprè s quoi aucune efficacité catalytique n'est observé e.Ré sultats supplé mentaires obtenus à 20 °C pour les diffé rents systè mes Au@polymè re.Les nanoparticules hybrides basé es sur des copolymè res statistiques pré sentent des valeurs de kobs plus é levé es que celles é valué es pour Au@PVCL et Au@PVP. De plus, un kobs optimal mesuré pour une teneur en VP est é gal à 50 %. La tendance observé e de l'efficacité catalytique en fonction de la composition du copolymè re pourrait ê tre rationalisé e comme un compromis entre deux effets opposé s. D'une part, une teneur plus é levé e en VCL augmentait le caractè re Ré sumé de thè se xi polymè res et les milieux aqueux ont radicalement changé . Cela entraî ne l'effondrement ou l'expansion des chaî nes polymè res. Il est inté ressant de noter que les proprié té s (telles que le Tc, l'auto-assemblage, etc.) des maté riaux thermosensibles sont influencé es non seulement par les paramè tres macromolé culaires d'un polymè re choisi (composition, masse molaire,

	architecture…), mais également par la polarité des composants hydrophiles ou hydrophobes
	incorporé s. comonomè res.
	Dans ce chapitre, nous avons cherché à é tudier plus avant les proprié té s des copolymè res
	de N-isopropylamide (NIPAM) et de monomè re hydrophobe d'acrylate de n-butyle (BA) à
	diffé rentes tempé ratures et concentrations de solution en relation avec leur composition et leur
	microstructure.
	VP dans le copolymè re infé rieure à 40%, il a é té possible d'augmenter la tempé rature de
	transition du maté riau hybride et d'amé liorer ses proprié té s catalytiques par rapport à des
	homologues comprenant des homopolymè res PVP et PVCL. De plus, l'incorporation d'une
	fraction plus é levé e d'unité s VCL dans les copolymè res VCL/VP favorise une stabilité
	colloï dale accrue des nanohybrides d'or.

hydrophobe de l'enveloppe organique entourant les AuNPs et favorisait ainsi la diffusion des ré actifs vers la surface des AuNPs. D'autre part, dans le mê me temps, la plus forte adsorption de VCL par rapport à VP limite l'efficacité catalytique des nanohybrides ré sultants. En ré sumé , l'effet de la composition a é té é valué à la fois sur la croissance des nanoparticules d'or synthé tisé es en pré sence des polymè res (voie in situ) et sur les proprié té s (stabilisation, optique, catalytique...) des nanoparticules pré formé es enrobé es par ces polymè res. Le caractè re hydrophobe accru du PVCL lui permet d'agir comme un agent de stabilisation et de contrôle de la croissance plus efficace que le PVP pour la synthè se in situ d'AuNPs. De plus, la copolymé risation statistique de VCL et de VP permet de moduler dans une certaine mesure les proprié té s du polymè re, et donc des maté riaux hybrides obtenus. A une fraction molaire de Chapitre III Les systè mes thermosensibles, obtenus en dissolvant un polymè re dans des solutions aqueuses, ont é té largement é tudié s. Ils pré sentent une tempé rature de transition caracté ristique appelé e tempé rature de point de trouble (Tc) à laquelle les interactions entre les chaî nes xi

Introduction

Chapter I. Literature Review

Chapter I. Literature Review

Scheme I.10 Micelle-to-(inverse micelle) transition of PMEMA-based pH-responsive copolymers in response to addition of salt and pH change.

Chapter II. AuNPs coated with P(VCL-stat-VP)20k

Chapter II. AuNPs coated with P(VCL-stat-VP)20k aminophenol in water using NaBH4 (Scheme II.3).[12] The color change of the system associated with the conversion of p-nitrophenol to p-aminophenol enables researchers to easily monitor the reaction kinetics by UV-vis spectroscopy at 400 nm. As expected, the catalytic reduction is not triggered when only NaBH4 is present.Scheme II.3 Reduction of p-nitrophenol to p-aminophenol by NaBH4 (system pH around 8).

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM) Figure III.2 1 H NMR spectra of (A) PBA2k-b-PNIPAM8k and (B) PBA5k-b-PNIPAM5k in CDCl3.

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter III. Thermoresponsiveness of P(BA-co-NIPAM)

Chapter IV. Thermo-and pH-responsiveness of PN-b-PD block copolymer

Chapter IV. Thermo-and pH-responsiveness of PN-b-PD block copolymer

Chapter IV. Thermo-and pH-responsiveness of PN-b-PD block copolymer

Chapter IV. Thermo-and pH-responsiveness of PN-b-PD block copolymer

Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer

Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer

Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer

Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer

Chapter V. Thermo-and CO2-responsiveness of PN-b-PD block copolymer

Conclusions

Acknowledgements

ii Acknowledgements……………………………………………………………...i Abbreviations…………………………………………………………………...v 182 Chapter IV. Thermo-and pH-responsiveness of PN-b-PD block copolymer upon which larger and stable spherical nanoobjects are formed. The presence of carboxylate function on the surface of these aggregates at least partially affects the colloidal stability of obtained nanoobjects.

I would like to thank China Scholarship Council (CSC) and Centre National de la Recherche Scientifique (CNRS) for the financial support of my Ph.D. project.

Abbreviations vi

Chapter II

(N-vinylcaprolactam / N-vinylpyrrolidone) statistical copolymers -Effect of copolymer composition on the formation, stabilization, thermoresponsiveness and catalytic properties of gold nanoparticles 126 Chapter III. Thermoresponsiveness of P(BA-co-NIPAM) conformation as a function of the architecture of copolymers at lower temperature. All results are reported in Table III III.3). In this case, the PNIPAM corona surrounding the PBA core is also swollen by the solvent. Its contribution to the SANS signal is very weak. Thus, with this assumption, the micelle radius deduced from SANS is the radius of the hydrophobic PBA core alone. The micelles radii of PNIPAM2.5k-b-PBA5k-b-PNIPAM2.5k copolymers measured by DLS and SANS are twice as large as those of PNIPAM4k-b-PBA2k-b-PNIPAM4k. Such an increase of micelle size related to the length of the hydrophobic block might be related to the strong aggregation limit case predicted and observed for the aggregation of diblock copolymer. [26] In this case, the hydrophobic blocks are mainly located in the core of the micelles. Longer hydrophobic block leads to the formation of micelles with a higher aggregation number and a For instance, Guan and co-workers designed a multi-stimuli responsive star polymer of tetraphenylethene-graf-tetra-poly(N-(2-(diethylamino) ethyl acrylamide) with an aggregationinduced effect, the obtained star polymer displays a good performance in long-term cell tracing.

[14] Kim and co-workers employed P(DEAEAM-r-NIPAM) as responsive surfactant to modulate particles shape of polystyrene-b-poly(4-vinylpyridine) between football and lens by subtly changing temperature and pH. [15] Then we studied the responsiveness of PDEAEAM-based block copolymers.

V.2 Dual CO2-and thermo-responsiveness of PD homopolymer

For polyamines, depending on the structure of amine groups and on the conditions of experiments, the reaction of amine function with CO2 leads to the formation of ammonium bicarbonates or carbamates. Most of (co)polymers with tertiary amine groups are prone to at higher temperature (41 o C). This result is also confirmed by DLS analysis, in which the aggregates size before, after exposure to CO2 and after bubbling N2 starts to increase at 32, 40 and 37 o C, respectively. Acryloyl chloride (72 mmol, 6 mL) dissolved in CHCl3 was added dropwise into flask within 1 h, after complete addition, the reaction was warmed up to room temperature for 4 h. Then the reaction mixture was washed with dilute NaOH solution and with deionized water three times, respectively. The organic phase was collected and concentrated under reduced pressure, the resulting residue was purified by aluminum oxide column chromatography (petroleum ether/ethyl acetate gradient 3 : 1 to 0 : 1, v/v) to give DEAEAM (5.39 g, yield: 53%). 1