Gabriela Bar-Nes

Radford Hall

Vikashni Sharma

Marianne Gaborieau

David Lucas

Patrice Castignolles

Robert G Gilbert
email: b.gilbert@uq.edu.au

Ansell Shah

Controlled/living radical polymerization of isoprene and butadiene in emulsion

Keywords: Emulsion polymerization, barrier products, RAFT, isoprene, butadiene, nanophase separation

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

INTRODUCTION

Personal barrier products (surgical and industrial rubber gloves, condoms) are currently manufactured using natural latex or emulsion polymerization synthesis methods that have evolved little in 50 years. Natural rubber latex possesses many desirable properties [START_REF] Blackley | Polymer Latices. 3. Applications of latices[END_REF] such as resource renewability, good film-forming and barrier-protection properties, plus high mechanical strength. However, there are several serious disadvantages, especially an allergic response that affects up to 17% of health professionals [START_REF] Phillips | Health care worker disability due to latex allergy and asthma: A cost analysis[END_REF], and the inability to 'fine-tune' the raw polymer in a way that effectively permits the engineering of the wide variations of properties possible with synthetic latexes. On the other hand, synthetic latexes (made by emulsion polymerization) do not have certain useful mechanical properties possessed by latexes made from natural rubber. In addition, one of the most commonly produced synthetic latexes is 'nitrile', the manufacture of which involves acrylonitrile, a very hazardous monomer. Moreover, neither natural nor synthetic latexes can currently produce a film with good impenetrability to both viruses and liquids, while still being permeable to water vapour so that they can 'breathe' and thereby minimize the accumulation of moisture on the skin-side of the glove.

A particular target for controlled syntheses of block copolymers is latexes wherein one page 3 monomer is isoprene or butadiene (both corresponding polymers having a very low glass transition temperature, T g ), and another is a monomer forming a polymer with a high T g , such as styrene. Isoprene is the monomer unit in natural rubber latex. Styrene-isoprene block copolymers have a wide range of well-ordered microphases [START_REF] Ruzette | Block copolymers in tomorrow's plastics[END_REF][START_REF] Holden | Thermoplastic Elastomers[END_REF][START_REF] Bodycomb | A Small-Angle X-ray Scattering Study of the Phase Behavior of Diblock Copolymer/Homopolymer Blends[END_REF][START_REF] Court | Morphological studies of binary mixtures of block copolymers: temperature dependence of cosurfactant effects[END_REF][START_REF] Han | Effect of microdomain structure on the order-disorder transition temperature of polystyrene-block-polyisoprene-block-polystyrene copolymers[END_REF][START_REF] Han | Effect of Volume Fraction on the Order-Disorder Transition in Low Molecular Weight Polystyrene-block-Polyisoprene Copolymers. 1. Order-Disorder Transition Temperature Determined by Rheological Measurements[END_REF][START_REF] Sakamoto | Ordering Dynamics of Cylindrical and Spherical Microdomains in Polystyrene-block-Polyisoprene-block-Polystyrene. 1. SAXS and TEM Observations for the Grain Formation[END_REF][START_REF] Soto-Figueroa | Molecular simulation of diblock copolymers; morphology and mechanical properties[END_REF][START_REF] Soto-Figueroa | Dissipative Particle Dynamics Study of Order-Order Phase Transition of BCC, HPC, OBDD, And LAM Structures of the Poly(styrene)-Poly(isoprene) Diblock Copolymer[END_REF][START_REF] Soto-Figueroa | Self-Organization Process of Ordered Structures in Linear and Star Poly(styrene)-Poly(isoprene) Block Copolymers: Gaussian Models and Mesoscopic Parameters of Polymeric Systems[END_REF][START_REF] Soto-Figueroa | Mesoscopic simulation of asymmetric-copolymer/homopolymer blends: Microphase morphological modification by homopolymer chains solubilization[END_REF], which vary with temperature and composition. Whilst barrier products can be made from anionically polymerized styrene-isoprene block copolymers, the products would typically be dipped from solvent solution. The solvents used in this process would typically be expensive, flammable and toxic. Barrier products are best cast from latexes, which are most conveniently synthesized by radical polymerization in emulsion [START_REF] Gilbert | Emulsion Polymerization: A Mechanistic Approach[END_REF]. A latex containing block copolymers of these monomers would lead to a nanostructured material due to the non-miscibility of polystyrene and polydienes. At low polystyrene contents and below the T g of polystyrene, the spherical nanodomains of high-T g polystyrene would act as physical crosslinks of the low-T g polydiene matrix, thus lead to thermoplastic elastomers [START_REF] Ruzette | Block copolymers in tomorrow's plastics[END_REF]. These physical crosslinks could be tailored by varying block lengths and comonomers ratio in the copolymer to obtain barrier products with desirable characteristics. Independently from these physical crosslinks, the uncontrolled 1,4 addition of the monomer occurring during the polymerization of the diene forms pending double bonds, which by further polymerization form chemical crosslinks within the diene matrix. Ideally, a synthetic process should be devised with minimal chemical cross-linking, so that the control of the microstructure of the block copolymer chain could allow tailoring the physical cross-linking and hence the material functional properties.

Controlled radical polymerization [START_REF] Braunecker | Controlled/living radical polymerization: Features, developments, and perspectives[END_REF][START_REF] Braunecker | Erratum to: "Controlled/living radical polymerization: Features, developments and perspectives[END_REF][START_REF] Lowe | Reversible addition-fragmentation chain transfer (RAFT) radical polymerization and the synthesis of water-soluble (co)polymers under homogeneous conditions in organic and aqueous media[END_REF][START_REF] Moad | Living Radical Polymerization by the RAFT Process[END_REF][START_REF] Moad | Radical addition-fragmentation chemistry in polymer synthesis[END_REF][START_REF] Perrier | Macromolecular design via reversible additionfragmentation chain transfer (RAFT)/Xanthates (MADIX) polymerization[END_REF] in dispersed media [START_REF] Save | Controlled radical polymerization in dispersed aqueous media (review)[END_REF][START_REF] Mcleary | RAFT mediated polymerisation in heterogeneous media[END_REF][START_REF] Charleux | Water-soluble SG1-based alkoxyamines: A breakthrough in controlled/living free-radical polymerization in aqueous dispersed media[END_REF] can be used to make block copolymers by radical polymerization, and thus has the potential to make barrier products with improved properties using less hazardous raw materials.

Controlled radical polymerizations of isoprene [START_REF] Benoit | Accurate Structural Control and Block Formation in the Living Polymerization of 1,3-Dienes by Nitroxide-Mediated Procedures[END_REF][START_REF] Murthy | Thermal shaping of shell-crosslinked (SCK) nanoparticles, facilitated by nanoconfinement of fluid-like cores[END_REF][START_REF] Wegrzyn | Preparation of poly(ethylene oxide)block-poly(isoprene) by nitroxide-mediated free radical polymerization from PEO macroinitiators[END_REF][START_REF] Lohmeijer | The LEGO Toolbox: Supramolecular Building Blocks by Nitroxide-Mediated Controlled Radical Polymerization[END_REF][START_REF] Cheng | Tandem Synthesis of Core-Shell Brush Copolymers and Their Transformation to Peripherally Cross-Linked and Hollowed Nanostructures[END_REF] and of butadiene [START_REF] Pradel | Controlled radical polymerization of 1,3butadiene. II. Initiation by hydrogen peroxide and reversible termination by TEMPO[END_REF] have been implemented using nitroxide-mediated radical polymerization, but the reported methods have the disadvantage of requiring relatively high temperatures. Although nitroxides which can be used at lower temperatures are now available [START_REF] Chauvin | Crowded Phosphonylated Alkoxyamines with Low Dissociation Temperatures: a Milestone in Nitroxide Mediated Polymerization[END_REF], the operating temperatures are still in the range at which chemical cross-linking of dienes becomes significant in radical page 4 polymerization [START_REF] Cheong | Synthesis and cross-linking of polyisoprene latexes[END_REF], which is often deleterious to desirable properties of a barrier film.

Reversible addition-fragmentation chain transfer (RAFT), on the other hand, can be often implemented at lower temperatures. However, RAFT-controlled radical polymerization of isoprene and butadiene is challenging, because of the low propagation rate coefficients of these monomers and because of the strength of the C-S bonds with these compounds means the fragmentation step in RAFT is undesirably slow. Nevertheless, conditions have been found [START_REF] Jitchum | Controlled Polymerization of isoprene via RAFT Polymerization[END_REF][START_REF] Germack | Isoprene polymerization via reversible addition fragmentation chain transfer polymerization[END_REF] whereby RAFT-controlled polymerization of isoprene has been successfully implemented, albeit in a very slow reaction process. There are no detailed literature reports of RAFT-controlled polymerization of butadiene.

A variety of methods are available to implement controlled radical polymerization in emulsion polymerization systems [START_REF] Save | Controlled radical polymerization in dispersed aqueous media (review)[END_REF][START_REF] Mcleary | RAFT mediated polymerisation in heterogeneous media[END_REF][START_REF] Charleux | Water-soluble SG1-based alkoxyamines: A breakthrough in controlled/living free-radical polymerization in aqueous dispersed media[END_REF][START_REF] Cunningham | Controlled/living radical polymerization in aqueous dispersed systems[END_REF], including those which can be used to make structured nanoparticles [START_REF] Nicolas | Nanostructured latex particles synthesized by nitroxide-mediated controlled/living free-radical polymerization in emulsion[END_REF][START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF]. We here use the method for implementing RAFT (reversible addition-fragmentation chain transfer) [START_REF] Moad | Living Radical Polymerization by the RAFT Process[END_REF][START_REF] Moad | Radical addition-fragmentation chemistry in polymer synthesis[END_REF] by RAFT-controlled self-assembly in the absence of added surfactant [START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF][START_REF] Ferguson | Effective Ab Initio Emulsion Polymerization Under RAFT Control[END_REF][START_REF] Bozovic-Vukic | SAN-b-P4VP Block Copolymer Synthesis by Chain Extension from RAFT-Functional Poly(4vinylpyridine) in Solution and in Emulsion[END_REF][START_REF] Rieger | Amphiphilic Poly(ethylene oxide) Macromolecular RAFT Agent as a Stabilizer and Control Agent in ab Initio Batch Emulsion Polymerization[END_REF][START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF]. In brief, this is as follows. One chooses a RAFT agent which is soluble in both polar solvents (typically water, propylene glycol or dioxane) and non-polar ones (such as hydrophobic monomer). One then commences the RAFT-controlled synthesis of a hydrophilic monomer (such as acrylic acid, AA) in either water or a convenient solvent such as dioxane, to a desired degree of polymerization (say, 5 -20). A hydrophobic monomer (e.g. styrene or n-butyl acrylate) is then added (after optional removal of most of the dioxane and redispersion in water, if dioxane is the original polymerization medium). The amount of hydrophobic monomer is best chosen so that there are no monomer droplets present [START_REF] Prescott | Successful Use of RAFT Techniques in Seeded Emulsion Polymerization: Living Character, RAFT Agent Transport and Rate of Polymerization[END_REF][START_REF] Prescott | RAFT in emulsion polymerization: what makes it different[END_REF] and also so that the next step of polymerization results in an amphiphilic species such as AA 5 -St 10 -RAFT) (St = styrene) which can undergo self-assembly into an entity such as a micelle. The interior of this is hydrophobic, in which the RAFT moiety will be compatible. Further hydrophobic monomer is then added to the resulting seed latex, so that polymerization continues in these new entities, which are typically monomer-swollen micelles wherein each oligomer/polymer contains a RAFT moiety and can thus continue polymerization. There is no added surfactant, with the acrylic acid component of the block page 5

copolymer providing electrosteric stabilization of the latex particles; this absence of added surfactant adds to the flexibility of the process, with regard to later formulation. The mechanisms involved in this procedure have been discussed elsewhere [START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF][START_REF] Sprong | Extended Mechanistic Description of Particle Growth in Electrosterically Stabilized Emulsion Polymerization Systems[END_REF]. An important problem that needs to be taken into account in implementing such a system is the fact that a retardation occurs for growth of smaller particles, stabilized by acrylic acid or poly(ethylene oxide) entities, arising from the formation of mid-chain radicals on these entities which are slow to propagate but quick to terminate [44][START_REF] Thickett | Mid-chain transfer to polymer in poly(butyl acrylate): direct evidence of retardative effects[END_REF][START_REF] Thickett | Mechanism of radical entry in electrosterically stabilized emulsion polymerization systems[END_REF][START_REF] Thickett | Emulsion Polymerization: State of the Art in Kinetics and Mechanisms[END_REF].

The RAFT agent chosen for this work is 2-[(dodecylsulfanyl)carbonothioyl]sulfanyl propanoic acid, Figure 1, which has previously been used successfully for RAFT-controlled emulsion polymerization, including showing good control with the starting monomer, acrylic acid [START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF][START_REF] Nguyen | Pigment Encapsulation by Emulsion Polymerization Using Macro-RAFT Copolymers[END_REF], and is readily made in a relatively pure form in large quantities. It has chemically similar leaving and stabilizing groups to one of the RAFT agents, 2ethylsulfanylthiocarbonylsulfanylpropanoic acid ethyl ester, also shown in Figure 1, successfully used previously [START_REF] Jitchum | Controlled Polymerization of isoprene via RAFT Polymerization[END_REF] for RAFT-controlled polymerization of isoprene in solution.

The overall strategy used in the present paper is as follows. We create an initial 'macroRAFT' reagent, comprising an acrylic acid oligomer (~ 10 units) using RAFT agent. This is further polymerized under RAFT control, usually starting with a few units of styrene (and sometimes with n-butyl acrylate), to create the hydrophobic component of the targetted block copolymer, undergoing RAFT-controlled self assembly in the process. A chosen amount of isoprene or butadiene is then added as the soft segment of the block copolymer. Thus the target is an acrylic acid-styrene-diene triblock copolymer synthesized in a latex particle. This block copolymer is expected to form spherical domains of polystyrene in the polydiene matrix due to the incompatibility of polystyrene and polydiene, and hence to yield a thermoplastic elastomer.

page 6

EXPERIMENTAL

Materials:

Acrylic acid (Sumika) (AA) was distilled to remove the inhibitor and kept in a freezer to prevent polymerization.

Synthesis of the seed by RAFT polymerization

For emulsion and solution polymerizations in flasks, the samples of acrylic acid (AA), styrene and isoprene were prepared as described elsewhere [START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF][START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF]; monomer was fed in with a syringe pump where appropriate. A 'macroRAFT', with a targetted composition of (AA) 10 -RAFT, was prepared in dioxane solution as described elsewhere [START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF], leading to high conversion (approx. 100%). Chain extension of the macroRAFT by the addition of styrene monomer was performed either in dioxane or propylene glycol solution, targetting AA 10 -St (5 or 10) -RAFT, or in emulsion, targetting AA 10 -St 40 -RAFT, using a RAFT to initiator molar ratio of 15:1 at 70 °C, overnight in a round-bottomed flask. The conversions of reaction carried out in solution were approx. 80%. The macroRAFT targetting 10 acrylic acid unit was analyzed using electrospray ionization mass spectrometry (ESI-MS; see Supporting Information). The ESI-MS data for this type of macroRAFT) exhibits a spectrogram with a maximum at the peak around 6-7 AA units instead of 10. This result may be an artifact because ESI-MS suffers from mass bias [START_REF] Martin | Why does matrix-assisted laser desorption/ionization time-of-flight mass spectrometry give incorrect results for broad polymer distributions?[END_REF].

Polymerization of polymers containing isoprene and butadiene via RAFT in emulsion

The seeds described previously were used for further polymerization of isoprene and butadiene both in a Mettler RC1e reactor and, for isoprene, also in round-bottomed flasks.

Experiments with the RC1e glass reactor were performed at 70 °C (isoprene) and 60 °C (butadiene) and with a RAFT: initiator molar ratio of 1:1 and conditions detailed in Tables 1 and2. A potential problem in reactions involving monomers which are gaseous (butadiene) or of low boiling point (isoprene) is cavitation under shear. Although the isoprene container was page 8

kept at 10 °C during the feeding, this did not completely prevent cavitation, because of the low boiling point of isoprene (34 °C at 1 atm). To limit this problem, the amount of isoprene was reduced after the first experiment.

For isoprene polymerizations, the pressure inside the RC1e reactor at 70 °C was kept stable during the whole reaction period and did not exceed 2-3 atm.

Batch emulsion polymerization of butadiene-containing polymers was performed in the RC1e reactor. The reactor was charged under argon with all chemicals present (except butadiene) before the initiator was added. Butadiene monomer (a gas at room temperature) was then transferred to the RC1e reactor with the vessel temperature at 25 °C and stirrer speed at 300 rpm. The temperature was then raised to the reaction temperature, after which the initiator solution was pumped into the reactor in order to initiate the polymerization.

Butadiene-containing syntheses were performed in the RC1e at 60 °C. This was a semi-batch system where the initial charge contained AIBN, styrene monomer, and RAFT diblock AA 10 -BA 15 -RAFT prepared by the same synthesis as above but with n-butyl acrylate, made in propylene glycol rather than in dioxane. After polymerization at 60 °C, the reactor was then cooled to 20 °C, butadiene was then fed in and the temperature raised back to 60 °C, and polymerization continued. Compositions are given in Table 2. The use of the RC1e permits the reaction to be monitored by measuring the heat flow.

Characterization of products

The conversions were measured gravimetrically, after drying the sample in the oven at 60 ºC.

Average particle sizes were measured using a Malvern HPPS. This device measures the z average of the particle size distribution, and like any light-scattering device applied to samples which have not been physically separated by size, it is well known that this cannot give unambiguous results for the actual particle-size distribution because the inversion of light scattering data to a distribution is an ill-conditioned problem (e.g. [START_REF] Berne | Dynamic Light Scattering[END_REF][START_REF] Vos | Quantitative Assessment of the Conditioning of the Inversion of Quasi-Elastic and Static Light Scattering Data for Particle Size Distributions[END_REF]). While a variety of size-separation techniques such as hydrodynamic chromatography and transmission page 9

electron microscopy can give the actual distribution, these are difficult to apply for the rubbery polymers which are the subject of the present investigation. For some runs, it was possible to obtain the full size distribution using hydrodynamic chromatography (Polymer Laboratories PSDA).

Electrospray mass spectrometry (ESI-MS) was used to characterize the molecular weight of the macroRAFT used as starting polymers, using the same conditions as Ferguson et al. [START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF].

Size-exclusion chromatography

Single-detection (differential refractive index) and dual detection (DRI and UV absorption) SEC was performed as described in [START_REF] Castignolles | High-Resolution Separation of Oligo(acrylic acid) by Capillary Zone Electrophoresis[END_REF] in tetrahydrofuran (THF) with 0.1 wt% trifluoroacetic acid (TFA) as eluent. The system was fitted with four Waters columns, HR 1 to 4, in series to allow a good separation from oligomers to average-size polymer chains; polystyrene standards were regularly injected and calibration curves constructed as in [START_REF] Nejad | Synthesis of methacrylate derivatives oligomers by dithiobenzoate-RAFT-mediated polymerization[END_REF] to check that separation was still operating according to a size-exclusion mechanism and that the separation by the columns was not loosing resolution. Sample concentrations ranged from 1-5 mg mL -1 . The detection wavelength of the UV detector was set at 290 nm to detect the RAFT moiety (Z-group) as in [START_REF] Castignolles | High-Resolution Separation of Oligo(acrylic acid) by Capillary Zone Electrophoresis[END_REF]. Complete recovery was assumed and the DRI and UV chromatograms were normalized so that the sum of the area of the macroRAFT and/or polymer signals is 1.

Differential scanning calorimetry

One of the methods used to characterize the morphology of the formed polymers was differential scanning calorimetry (DSC).This used either a Mettler DSC 2920 MDSC v. 2.6A

under the following conditions (heat-cool-heat cycle): heat to 180 °C at 10 °C min -1 , cool to -80 °C at a rate of -10 °C min -1 , then heat again to 180 °C at a rate of 10 °C min -1 (Figures 4 and5). Another DSC measurement used a TA Instruments DSC Q2000 and the following temperature program: heat at 3 ºC⋅min -1 from -60 to +100 ºC, isothermal at +100 ºC for 5 min, page 10 cool at -3 ºC⋅min -1 from +100 to -60 ºC, then heat at 3 ºC min -1 from -60 to +100 ºC under an N 2 flow rate of 50 mL⋅min -1 , on dry samples of mass 6-8 mg.

Solid-state NMR

Solid-state 13 C NMR was also used to characterize the morphology of the formed polymers.

Spectra were recorded on a Bruker Avance 300 wide-bore spectrometer (Bruker Biospin Pty Ltd.), operating at a Larmor frequency of 75 MHz for 13 C, using a 4 mm magic-angle spinning (MAS) probe (Bruker Biospin Pty Ltd.), operated with XWIN-NMR software (Bruker Biospin GmbH). The sample was ground to a fine powder, packed in a high-speed 4 mm zirconia rotor and spun at 4.5 kHz MAS at room temperature. A 13 C single-pulse excitation (SPE-MAS) spectrum was recorded with a 3.6 µs 90° pulse and continuous wave decoupling (optimized on adamantane); 38336 transients were recorded with a delay of 3 s between scans, for a total experimental time of 34 h. 13 C cross-polarization (CP-MAS) spectra were recorded with a 3.38 µs 1 H 90° pulse, continuous wave decoupling (optimized on adamantane), 2048 transients, a delay of 3 s between scans and contact times of 0.2, 0.5, 1, 2, 3 and 4 ms contact time respectively (experimental time ca 1 h 50): similar line shapes were obtained, thus the contact time of 1 ms was selected as the one giving the highest intensity.

The chemical shift scale was externally calibrated with respect to the resonance of adamantane at 38.48 ppm [START_REF] Morcombe | Chemical shift referencing in MAS solid state NMR[END_REF]. 13 C chemical shifts of both polyisoprene and polystyrene are known from literature [START_REF]NMR spectra database of polymers[END_REF].

RESULTS AND DISCUSSION

The ab-initio RAFT in emulsion process [START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF] 1).

Styrene chain extension in emulsion

The addition of styrene to the macroRAFT was carried out in emulsion (Run GB237_024) [START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF], where 5 % of BA was added to the styrene, because of favourable reactivity with the RAFT agent. Dual-detection SEC analysis was carried out on the resulting AA 10 -(St 38random-BA 2 )-RAFT. This is the first such dual-detection characterization of a product prepared by RAFT-controlled self assembly in emulsion, and the result shows two elution peaks (Figure 2; see also Supporting Information for a corresponding examination of the chain extension of styrene in solution). The peak at longer elution times corresponds to the macroRAFT precursor. A new peak appears at shorter elution times after polymerization, showing chain extension. Comparing the signals from the refractive index and the UV detectors shows that both peaks contain the RAFT Z group, i.e. are living. A possible reason for the appearance of two peaks may be that the AA 10 -C 12 macroRAFT does not form micelles and the particles are thus obtained with this macroRAFT by a pure and slow homogenous nucleation mechanism [START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF].

To ensure that most of the emulsion polymerization occurs inside micelles, we added an additional synthesis step to create a longer hydrophobic chain: a few (5 to 12) units of styrene were added to the macroRAFT in solution (dioxane). The resulting amphiphilic oligomer was then used (dispersed in water) as the 'seed' for subsequent ab initio emulsion polymerization.

RAFT-controlled polymerization of isoprene and butadiene in solution

Previous studies of RAFT-mediated polymerization of isoprene were performed in solution or bulk. Here, we perform RAFT-mediated solution polymerization of isoprene for two reasons:

page 12
to compare the degree of control/livingness and polymerization rate with our macroRAFT agent (which is slightly different from that used previously [START_REF] Jitchum | Controlled Polymerization of isoprene via RAFT Polymerization[END_REF]), and also to prepare RAFTcapped AA-styrene diblocks which can subsequently be used in RAFT-controlled self assembly in emulsion.

Isoprene solution polymerization in dioxane, starting with AA A shift is observed in the plots after the addition of isoprene to the AA 10 -St 12 -RAFT. This suggests that some isoprene has been added. This small shift is consistent with the number of isoprene monomer units in the recipe: 22 units (corresponding to 56 % conversion, 40 units were targeted for 100 % conversion). The large peak around the elution time of 43 minutes in the UV may be due to degradation of the RAFT agent [START_REF] Nejad | Synthesis of methacrylate derivatives oligomers by dithiobenzoate-RAFT-mediated polymerization[END_REF].

The efficiency of the initiation of isoprene polymerization by the macroRAFT agent cannot be determined quantitatively from the SEC results, even using double detection, because molecular weights can not be determined. Apparent (polystyrene-equivalent) molecular weights have recently shown to be misleading to study control/living polymerization [START_REF] Guillaneuf | Using apparent Molecular Weight from SEC in controlled/living polymerization and kinetics of polymerization[END_REF] (apparent molecular weights can indicate a very poor control for a well-controlled polymerization, and vice-versa). As is well known, SEC of a branched polymer cannot give molecular weight, since SEC separates by size (hydrodynamic volume, V h ) not molecular weight, and polymers with different molecular weights and different branching structures can have the same V h [START_REF] Kostanski | Size-exclusion chromatography -a review of calibration methodologies[END_REF][START_REF] Gaborieau | Theory of multiple detection size exclusion chromatography of complex branched polymers[END_REF][START_REF] Gaborieau | Separation of complex branched polymers by size-exclusion chromatography (SEC) probed with multiple detection[END_REF][START_REF] Castignolles | Detection and quantification of branching in polyacrylates by size-exclusion chromatography (SEC) and melt-state 13C NMR spectroscopy[END_REF]. Under special circumstances, which need to be ascertained for each particular system, quantitative information about the efficiency of initiation (i.e. percentage of polymer chains containing isoprene) can be obtained from MALDI ToF mass spectrometry [START_REF] Willemse | Copolymer Fingerprints of Polystyrene-block-polyisoprene by MALDI-ToF-MS[END_REF]. This was not however attempted here.

The T g of polyisoprene depends on the polymer microstructure (the amounts of 1,4-, 1,2-and 3,4-structures, and the amounts of cis and trans) [START_REF] Kow | Glass transition behavior of polyisoprene: the influence of molecular weight, terminal hydroxy groups, microstructure, and chain branching[END_REF]. 1,4 cis polyisoprene has a T g ~ -70 °C, while 1,4 trans has T g ~ -60 °C [START_REF]Polymer Handbook[END_REF]. The polymer prepared by radical polymerization is expected to be a mixture of cis and trans, and of 1,4 and other isomers. fact that the T g corresponding to the polystyrene-rich phase is shifted from 90 °C down to ca 50 °C by the addition of isoprene shows that the polystyrene-rich phase probably contains a significant amount of isoprene monomer units. The AA 10 -St 12 -I 42 -RAFT sample exhibits a isoprene:styrene monomer ratio significantly larger than 1. Considering the known evolution of the nanostructure morphology with the volume fraction of comonomer units in a PS-PI block copolymer [START_REF] Khandpur | Polyisoprene-polystyrene diblock copolymer phase diagram near the orderdisorder transition[END_REF], this sample's morphology may be spherical (or cylindrical) polystyrene-rich nanodomains in a polyisoprene-rich matrix.

The combination of double detection SEC with DSC shows that the chosen RAFT agent can be used to form isoprene-and styrene-based block copolymers and that the materials exhibit the desired nanostructure, in which polystyrene-rich nanodomains act as physical crosslinks within the polyisoprene-rich matrix. This RAFT agent thus could be used for the synthesis of isoprene-based rubber with a physical crosslinking due to polystyrene-rich regions [START_REF] Ruzette | Block copolymers in tomorrow's plastics[END_REF].

Isoprene addition in emulsion

The SEC data for consecutive samples are given in Figure 6, where the original material was AA 10 -RAFT and the final target was AA 10 -St 45 -I 80 -RAFT.

The continuation of macroRAFT polymerization with isoprene in emulsion (VS211_25 and VS211_32) gives very high conversions in a short time. This is in contrast to the observation of Jitchum and Perrier [START_REF] Jitchum | Controlled Polymerization of isoprene via RAFT Polymerization[END_REF], who showed a conversion of 5, 14 and 40% with reactions at 60, 90 and 115 ºC in 30 h. Termination does not seem to be the main reason for this difference because the rate of this process is similar in solution and emulsion, and indeed often greatly reduced in emulsion because of compartmentalization (isolation of the radicals in separate particles). The propagation rate coefficient, k p , of isoprene is probably low; there are no reliable data for this quantity in the literature, but there is a report of this quantity for butadiene, obtained by pulsed-laser polymerization [START_REF] Bandermann | Towards the propagation rate coefficient for the free-radical polymerization of 1,3-butadiene[END_REF] (the only reliable method for obtaining values of k p [START_REF] Asua | Critically evaluated rate page 27 coefficients for free-radical polymerization, 5 ). Propagation rate coefficient for butyl acrylate[END_REF][START_REF] Beuermann | Critically evaluated rate coefficients for free-radical polymerization, 4; Propagation rate coefficients for methacrylates with cyclic ester groups[END_REF][START_REF] Beuermann | Critically evaluated rate coefficients for free-radical polymerization, 3. Propagation rate coefficients for alkyl methacrylates[END_REF][START_REF] Beuermann | Critically evaluated rate coefficients for free-radical polymerization, 2. Propagation rate coefficients for methyl methacrylate[END_REF][START_REF] Buback | Critically evaluated rate coefficients for free-radical polymerization, 1. Propagation rate coefficients for styrene[END_REF]) and these butadiene studies suggest a low k p . While this low page 15

k p certainly contributes to the slow rate of polymerization in solution, this effect is of course also applicable to polymerization in emulsion.

Another contributing factor to the slow polymerization in solution might be ascribed to the occurrence of abstraction and/or transfer reactions on the backbone [START_REF] Moad | The Chemistry of Free Radical Polymerization 2nd Edn[END_REF][START_REF] Anstey | Using mechanisms to make seemingly impossible latexes and polymers[END_REF][START_REF] Lamb | Modification of natural and artificial polymer colloids by "topology-controlled" emulsion polymerization[END_REF][START_REF] Kangwansupamonkon | Kinetics of surface grafting reaction on polyisoprene latexes by reaction calorimetry[END_REF][START_REF] Lee | Structure-Property Relationships in Modified Natural Rubber Latexes Grafted with Methyl Methacrylate and Vinyl neodecanoate[END_REF], producing an allylic-type radical which is slow to propagate but quick to terminate; again, this process is present in both emulsion and solution systems, but may be reduced in emulsion systems where radical compartmentalization in particles is significant (such as 'zero-one' systems [START_REF] Gilbert | Emulsion Polymerization: A Mechanistic Approach[END_REF][START_REF] Van Herk | Emulsion Polymerisation[END_REF]). However, in well understood styrene emulsion systems growing under RAFT control, the observation is that there is a slight, but not enormous, decrease in rate compared to an equivalent solution system, which arises from a number of reasons [START_REF] Prescott | Successful Use of RAFT Techniques in Seeded Emulsion Polymerization: Living Character, RAFT Agent Transport and Rate of Polymerization[END_REF][START_REF] Prescott | RAFT in emulsion polymerization: what makes it different[END_REF][START_REF] Prescott | Chain-Length Dependence in Living/Controlled Polymerizations: Physical Manifestation and Monte Carlo Simulation of Reversible Transfer Agents in Emulsion Polymerization[END_REF][START_REF] Prescott | Average termination rate coefficients in emulsion polymerization: effect of compartmentalization on free-radical lifetimes[END_REF][START_REF] Prescott | Radical loss in RAFT-mediated emulsion polymerizations[END_REF][START_REF] Prescott | Rate optimization in controlled radical emulsion polymerization[END_REF], all of which would be expected to be applicable to isoprene. In this context, it is noted that while compartmentalization (reduction in termination rate arising from the isolation of radicals within particles) can increase the rate in zero-one emulsion polymerizations, this can be counteracted in RAFT systems by exit of z-meric entering radicals before they propagate [START_REF] Prescott | Rate optimization in controlled radical emulsion polymerization[END_REF].

The occurrence of retardation through the formation of mid-chain radicals in the AA stabilizing layer would also decrease the rate in emulsion [44][START_REF] Thickett | Mid-chain transfer to polymer in poly(butyl acrylate): direct evidence of retardative effects[END_REF][START_REF] Thickett | Mechanism of radical entry in electrosterically stabilized emulsion polymerization systems[END_REF][START_REF] Thickett | Emulsion Polymerization: State of the Art in Kinetics and Mechanisms[END_REF].

The most reasonable explanation for the increase in rate observed here in emulsion polymerization of isoprene relative to solution is an increase in the rate of initiation: specifically, an increase in the rate coefficient for entry of radicals from the aqueous phase into the interior of particles. Isoprene is known to have a very low reactivity and this is generally attributed to a very low initiation rate. Jitchum and Perrier's system is strictly a homopolymerization: isoprene is the only monomer involved. On the contrary, our emulsion polymerization seed contains some residual styrene monomer. This styrene may in our case significantly increase the entry rate in our emulsion polymerization system and thus increase the overall rate of polymerization. The reason for the possible increase in initiation rate can be found in the mechanism of entry in emulsion polymerization: one of the rate-determining steps for entry is the aqueous-phase propagation to a species which is surface active and capable of entry, a z-mer [START_REF] Maxwell | The entry of free radicals into latex particles in emulsion polymerization[END_REF][START_REF] Van Berkel | Entry in Emulsion Polymerization: Effects of Initiator and Particle Surface Charge[END_REF]. Isoprene, being very slow to propagate, would have very page [START_REF] Braunecker | Erratum to: "Controlled/living radical polymerization: Features, developments and perspectives[END_REF] low initiator efficiency in emulsion because of termination in the aqueous phase (propagation to z-mers), in addition to the slow rate of addition to an initiator-derived radical which is probably responsible for the slow rate in solution. However, if there is some residual styrene monomer, then the small amount in the water phase can form z-mers more efficiently because styrene propagates more rapidly than isoprene (an effect which has been seen in other systems [START_REF] De Bruyn | Starch-graft-(synthetic copolymer) latexes initiated with Ce4+ and stabilized by amylopectin[END_REF]). Hence the initiator efficiency will probably be higher in the presence of small amounts of styrene.

Further polymerization of the previously described seeds (VS211_65) in emulsion leads after 2 h to a product which insoluble in THF and in THF + TFA (VS211_66). In THF + TFA, very fine needle-like particles could be seen. Filtering this followed by SEC characterization showed that the peak of the product with isoprene (VS211_66) did not move from that of the product with styrene (VS211_65), but there was also an additional peak in the VS211_66 sample eluting at approximately 20 min.

Table 3 shows the z-average particle sizes of various products from emulsion polymerizations. The average particle size does not change much after the addition of the isoprene. The z-average particle size are around 11 -12 nm in diameter; note that the precision of HPPS with this device is not high for such small particles. Also shown in this table are the number-average particle sizes that would be expected from the observed composition, assuming ideal mixing (i.e., that the volume of the copolymer is the same as the sum of volumes of the same entities as homopolymers, in the appropriate molar ratio). It is noted that the z average of a distribution is always greater than its number average.

From Table 3, it can be seen that, for VS211_32, the experimental z-average radius of the seed VS211_31 after isoprene polymerization is lower than that before isoprene polymerization. Reduction of the size of the particles after diene polymerization is consistent with chemical crosslinking of isoprene in the latexes and/or non-ideal mixing. This has been reported for butadiene in emulsion made by conventional emulsion polymerization [START_REF] Weerts | Kinetic aspects of the emulsion polymerization of butadiene[END_REF] and will be also seen to occur with the present butadiene system, an emulsion polymerization in the presence of a RAFT agent (see below).

page 17

Insoluble products from the isoprene addition syntheses were characterized by DSC. The DSC data for sample GB237_49 are shown in Figure 7. During the first heating, a T g is observed at ca. -25 °C; during the second heating, a T g is observed at ca. 80 °C (note that there is a large uncertainty on that value due to the low intensity of the transition). It is emphasized that the T g at ~80 °C could not be observed during the first heating, as it would be masked by the intense water melting transition at ca. 85 °C. Furthermore, the T g at ca. spectrum, while signal B is significantly more intense in the SPE-MAS spectrum. This shows that the polyisoprene comonomer units are significantly more mobile than the polystyrene ones. It indicates a nanophase separation between a polystyrene-rich and a polyisoprene-rich regions within the sample. Note that the resolution of the SPE-MAS spectrum is insufficient to allow a quantification of the relative amounts of the three comonomer units; this may be due to the overall rigidity of the sample and the high density of signals in the 10 to 50 ppm region. The resolution could be increased by increasing the chains mobility via a strong increase in temperature [START_REF] Castignolles | Detection and quantification of branching in polyacrylates by size-exclusion chromatography (SEC) and melt-state 13C NMR spectroscopy[END_REF], but this was not attempted here because the RAFT agent would not be stable in these conditions.

A nanophase separation between a polystyrene-rich and a polyisoprene-rich phases is revealed in sample GB237_49 by two distinct T g 's observed by DSC, and by different mobilities of the components observed by solid-state NMR. The average composition of the sample would be AA 10 -St 40 -I 46 -RAFT based on conversion measured by gravimetry.

However, SEC of the similar but soluble sample VS211_78 (Figure 6) shows little addition of isoprene to the AA-St-RAFT precursor under similar conditions, as shown by the small shift of SEC signal compared to AA-St-RAFT precursor. Hence the sample is expected to have much less than 46 monomer units of isoprene in average, and thus this sample is mainly composed of the high-T g polystyrene. This is in agreement with the overall strong rigidity of the sample observed by solid-state NMR. With a isoprene:styrene monomer ratio significantly smaller than 1 in sample GB237_49, the expected morphology is spherical (or possibly cylindrical) polyisoprene-rich nanodomains in a polystyrene-rich matrix. Thus a nanostructured sample was successfully obtained by emulsion polymerization of polystyrene and polyisoprene.

Butadiene addition in emulsion

Because butadiene addition was performed in the RC1e reactor, it is possible to obtain rate information from the calorimetric capabilities of this reactor. Heat-flow data were obtained for the emulsion polymerization of butadiene grown under conditions expected to lead to page 19

RAFT-controlled self-assembly, starting with a acrylic acid/n-butyl acrylate/RAFT diblock, feeding first styrene and then butadiene so that a block copolymer might be anticipated.

Results are shown in Figures 9 (styrene growth step) and 10 (butadiene growth step). The styrene addition step shows the expected initial rapid rate rise, followed by an approximately steady state growth until the styrene feed is stopped, whereupon the rate rapidly decreases; this suggests that styrene growth is essentially under starved conditions. The butadiene addition instead shows a very slow rate after an initial rapid rise.

This very slow rate can be explained by the effects discussed for the corresponding isoprene system, detailed in the preceding section. Because there was no significant residual styrene monomer available to improve entry efficiency, the slow rate is ascribed to the low propagation rate coefficient combined with low initiator efficiency.

Characterization data are given in Figures 11 (SEC and that instead most of the butadiene polymerization produced much larger chains. One would expect significant branching in the radical polymerization of polybutadiene at 60 °C, and combination of growing branches can also lead to a cross-linked system. However, the latex dissolves easily in THF, which would indicate a low gel fraction: thus, while significant branching may occur (which would of course explain the high molecular weight component), it is not so extensive as to result in cross-linking.

page 20

It was possible for this sample to obtain the full particle size distribution (PSD) using hydrodynamic chromatography, the z-average could be calculated from the observed PSD and compared with the z-average inferred from light scattering of the unseparated sample, as

shown in Table 3. The slight difference in these z-average values is within the experimental uncertainties of the two techniques. The PSD seems to show that there are significant numbers of particles which are smaller than the parent seed, which suggests some secondary particle formation. While this is possible, it cannot be checked by electron microscopy because of the difficulties in obtaining good images of very small particles with very low T g ; moreover, the shape of the component of the distribution at smaller sizes is very sensitive to numerical artifacts in the deconvolution algorithm used in the PSDA [START_REF] Nagy | Resolution in Column Chromatography of Polymer latices. I. The light Scattering behaviour of Polystyrene and Its Effect on Signal Resolution in HDC[END_REF][START_REF] Mchugh | Particle size analysis by chromatography[END_REF][START_REF] Ishige | Solution of Tung's axial dispersion equation by numerical techniques[END_REF], as well as to assumptions made in data processing concerning optical uniformity of the particles.

As seen with isoprene, the observed particle size after butadiene polymerization (Table 3) was much less than would be predicted from simple volume additivity: non-ideal behaviour which can be ascribed to the occurrence of cross-linking and/or branching.

While hydrodynamic volume was not quantified here, the SEC data show clearly that there is a large amount of chains with much higher hydrodynamic volume than would be if the sample had grown entirely under controlled conditions.

CONCLUSIONS

It was found that synthesis of block copolymers of isoprene or butadiene in emulsion polymerization using RAFT is very hard to achieve. Much of the polymerization results in loss of molecular weight control, although some control is apparent. Moreover, there is often significant cross-linking, and the reactions are slow.

The slow rate can be ascribed to the following reasons. First, the monomers have low propagation rate coefficients, making the reactions slow, and thereby increasing the relative amounts of undesirable side reactions, particularly aqueous-phase termination prior to entry of an initiator-derived radical into the particle. Second, these monomers readily undergo abstraction and/or transfer to form an allylic radical structure on the main chain, which is slow page 21

to propagate but probably quick to terminate, and which can also lead to branching and crosslinking. RAFT control itself is difficult because the strength of the C-S bond formed between the RAFT agent and the diene makes the fragmentation step in the RAFT mechanism much slower than in monomers such as acrylates. The emulsion polymerization of isoprene is however faster than corresponding solution polymerization, an observation which can be explained by the presence of a small amount of a monomer such as styrene which forms aqueous-phase radicals which can enter particles much more efficiently than those from the dienes. The rate in emulsion polymerizations would presumably be even faster if one could choose a stabilizing system which would avoid retardation due to the mid-chain radical effect present with stabilizers based on acrylic acid or poly(ethylene oxide) [44][START_REF] Thickett | Mid-chain transfer to polymer in poly(butyl acrylate): direct evidence of retardative effects[END_REF][START_REF] Thickett | Mechanism of radical entry in electrosterically stabilized emulsion polymerization systems[END_REF][START_REF] Thickett | Emulsion Polymerization: State of the Art in Kinetics and Mechanisms[END_REF].

Despite the low level of molecular weight control ('livingness') seen in these systems, the polymers do have some interesting properties. The chosen RAFT agent can be used to form isoprene-and styrene-based block copolymers, and DSC and solid-state NMR data suggest that the materials have a nanostructure with a phase separation into high-T g polystyrene-rich domains and low-T g polyisoprene-rich domains. This RAFT agent thus could be used for the synthesis of isoprene-based rubber with a physical crosslinking due to polystyrene-rich regions [START_REF] Ruzette | Block copolymers in tomorrow's plastics[END_REF]. This has the potential to lead to barrier materials with novel physical properties.

Future work can be aimed at optimizing the degree of control by seeking out initiation systems and temperatures which can minimize the abstraction/transfer processes [START_REF] Cheong | Synthesis and cross-linking of polyisoprene latexes[END_REF][START_REF] Kangwansupamonkon | Kinetics of surface grafting reaction on polyisoprene latexes by reaction calorimetry[END_REF].

Polymerization rates can be increased by adding small quantities of a monomer with a high entry efficiency in emulsion polymerizations. Figure 3 gives SEC analysis of one of the products (GB237-034) compared to the macroRAFT from which it was prepared (GB237-033). Chain extension is seen by the shift of the peak to smaller elution times (top compared to bottom graphs of Figure 3). Comparison between DRI and UV spectra shows qualitatively that the diblock is "living". The product of reaction GB237-034 was reacted further in emulsion with 40 units of styrene to give AA 10styrene 45 -RAFT (GB237-035), which was later reacted with isoprene in emulsion.

Solution polymerization of butadiene with RAFT agent

Solution polymerization of butadiene in toluene at 60 ˚C for 20 h in the presence of C 12 RAFT agent gave low conversion: 5%. One reason for the slowness of the rate may be ascribed to the fact that the reaction was in the presence of a C RAFT agent, rather than a styrene-ended macro-RAFT. The SEC results for samples taken at initial and final times over the duration of the run are given in Figure 4. The formed polymer has two peaks, at low and high molecular weight. The low molecular weight peak shows a small increase in peak molecular weight with conversion, indicating that this component was probably under RAFT control. The SEC data for the high molecular weight component, the peak of which shows no increase in time and whose proportion of total polymer grows with conversion, indicates that much of the polymerization is not under RAFT control.

Figure 3

 3 shows the dual-detection SEC results of the macroRAFT (VS211_65, AA 10 -St 12 -RAFT), and the reaction products of this macroRAFT with successive polymerization of isoprene in dioxane solution, VS211_68 (1) and VS211_68[START_REF] Phillips | Health care worker disability due to latex allergy and asthma: A cost analysis[END_REF]. The SEC distribution of the parent RAFT agent used in the reaction is also shown.The SEC results show that there is chain extension with the addition of isoprene. Comparing the DRI with the UV signals shows that the reaction product contains the RAFT Z-group, indicative of some livingness. However, closer examination of the RAFT peak detected by UV (around 42 min in elution time) shows that for all of the products (including the macroRAFT), most of the RAFT molecules remained unreacted. This was not observed before since the mass fraction of unreacted RAFT molecules is becoming rapidly negligible as shown by the DRI detector. However, the use for the first time on this process of UV detection shows incomplete reactivity of the RAFT, which seems to originate from the first synthetic step, i.e. the production of the AA 10 -RAFT macroRAFT. This thus applies to most ab-initio RAFT systems[START_REF] Ferguson | Ab Initio Emulsion Polymerization by RAFT-Controlled Self Assembly[END_REF][START_REF] Ferguson | Effective Ab Initio Emulsion Polymerization Under RAFT Control[END_REF][START_REF] Ganeva | Particle Formation in ab Initio RAFT Mediated Emulsion Polymerization Systems[END_REF][START_REF] Sprong | Extended Mechanistic Description of Particle Growth in Electrosterically Stabilized Emulsion Polymerization Systems[END_REF].page[START_REF] Soto-Figueroa | Mesoscopic simulation of asymmetric-copolymer/homopolymer blends: Microphase morphological modification by homopolymer chains solubilization[END_REF]

Figure 4 and 5

 5 show the DSC results obtained for samples VS211_65 (targetting AA 10 -St 12 -RAFT) and Figure5shows DSC data for VS211_68 (2) (targetting AA 10 -St 12 -I-RAFT). There is clearly a single T g corresponding to polystyrene (and poly(acrylic acid)) around 90 °C for the AA 10 -St 12 -RAFT sample. For the sample containing isoprene, one sees two separate glass transitions.The first at -50 °C corresponding to the polyisoprene segment, and the second signal around 50 °C, corresponding to polystyrene. This result is consistent with the presence of two separate phases in our product: one polyisoprene-rich and the other one polystyrene-rich. The page 14

  -25 °C could not be observed during the second heating, as it is masked by the fluctuation of the signal at lower temperatures. Such signal fluctuations are commonly observed in DSC at temperatures just above the lowest measured temperature, and they mask the T g at ca. -25 °C in this work because of its low intensity (this difficulty might perhaps be eliminated by starting the DSC measurement at much lower temperatures, typically 100 °C below the lowest observed transition). It is concluded that this sample exhibits two T g 's, at ca. -25 °C and at ca. 80 °C. This result is consistent with the presence of two separate phases in our product: one polyisoprene-rich and the other one polystyrene-rich. The fact that the T g corresponding to the polyisoprene-rich phase is shifted from -50 °C (see above) up to ca. -25 °C by the presence of polystyrene shows that the polyisoprene-rich phase probably contains a significant amount of styrene monomer units.The nanostructure of sample GB 237_49 was further examined by solid-state NMR. Two types of13 C spectra were recorded: CP-MAS and SPE-MAS, which are respectively more sensitive to rigid and mobile species. Similar signal-to-noise ratios are obtained for the SPE-MAS in 34 h and for the CP-MAS spectrum in 2 h (Figure8), while a factor of 4 would be expected from the difference in measuring time alone. This indicates an overall strong rigidity of the sample. Further information can be deduced from the relative intensities of the signals. Due to the relatively similar structure of isoprene and styrene, most signals in the 13 C spectrum actually contain overlapping signals from the two comonomer units. The two exceptions are signal A at 146 ppm, which contains only the aromatic carbon of polystyrene linked to the backbone, and signal B at 31 ppm, which contains only CH 2 signals from polyisoprene. Relative to other signals, signal A is significantly more intense in the CP-MAS page 18

  ) and 12 (size distribution). The styrene stage showed molecular weight very close to the expected values, indicating polymerization under RAFT control. The butadiene stage, on the other hand, showed a slight broadening of the polystyrene peak and a new peak at very high molecular weight. Solids and particle size increases indicate polymerization took place. If the system were under good RAFT control, then given the amount of butadiene polymerized, the size distribution of the second-stage polymerization should show the usual pronounced shift of the peak towards higher size. The observation of very little change in the smaller component of the size distribution (growth from the styrene-RAFT macroRAFT) suggests that the butadiene polymerized with little or no molecular weight control within the particles already formed,

Figure 2 .

 2 Figure 2. Dual-detector SEC data for a AA10-(St38-random-BA2)-RAFT macroRAFT (run GB237_024, top) and its AA10-RAFT macroRAFT precursor (run GB237_019, bottom,), showing the living character of the C12-RAFT agent with AA and styrene in emulsion.

Figure 3 .

 3 Figure 3. Dual-detection SEC data for experiments designed to produce styrene-isoprene diblock copolymers in dioxane solution. RAFT agent, VS211_64, VS211_65, VS211_68 (1) and VS211_68 (2). Top panel: DRI, bottom panel: UV detector.

Figure 4 .

 4 Figure 4. DSC data for VS211_65 (AA10-St12-RAFT). Both the heat flow and the derivative are shown.

Figure 5 .

 5 Figure 5. DSC data for VS211_68 (2) (AA10-St12-I42-RAFT). Both the heat flow and the derivative are shown.

Figure 6 .

 6 Figure 6. Dual-detection SEC data for VS211_72, VS211_73, VS211_74, VS211_78, VS211_88, targetting AA10-St45-I80-RAFT in emulsion polymerization

Figure 8 .

 8 Figure 8. 13 C SPE-MAS (top) and CP-MAS (bottom) NMR spectra of sample GB237_49. Asterisks indicate spinning side bands, and the large underlying signal centred around 130 ppm in the SPE-MAS spectrum is a background signal coming from the probe.

Figure 9 .

 9 Figure 9. Heat-flow data for the styrene addition step of Run RH_45, targeting AA10-BA25-St15-RAFT. The arrows indicate the beginning and ending of the styrene feed.

Figure 10 .

 10 Figure 10. Heat-flow data for the butadiene addition step of Run RH_45, targeting AA10-BA25-St150-Bu250-RAFT. The butadiene feed commences at about 6 h.

Figure 11 .

 11 Figure 11. SEC data (DRI detector) for starting and final polymer from Run RH_45, which aimed to form a styrene-butadiene block copolymer using RAFT-controlled self assembly in emulsion. Data are plotted as functions of polystyrene-equivalent molecular weight, which is the molecular weight of polystyrene which has the same hydrodynamic volume as the chains eluting at a given elution time; it is emphasized that this is not the actual molecular weight of the sample.

Figure 12 .

 12 Figure 12. Particle size distribution data for starting and final latexes from Run RH 45, which aimed to form a styrene-butadiene block copolymer using RAFT-controlled self assembly in emulsion.

Figure 1 :

 1 Figure 1: NMR spectrum of C 12 RAFT agent. The 1 H chemical shifts of the RAFT agent were estimated using the ChemDraw Ultra 10.0 software (CambridgeSoft). The experimental 1 H NMR spectrum is in good agreement with the estimated one, apart from very minor impurities at 2.9 and 4.5 ppm, and acetone (used to rinse the NMR tube) at 2.15 ppm.

Figure 2 :

 2 Figure 2: Electrospray ionization MS results for VS211_64.

Figure 3 .

 3 Figure 3. Dual-detection SEC characterization of GB237-034 (top), a macro-RAFT AAstyrene diblock formed by chain extension of a smaller diblock (GB237-033, bottom) in solution.

Figure 4 .

 4 Figure 4. SEC (DRI detection) of product taken at various times from butadiene polymerization in toluene solution with C 12 RAFT agent. Data are plotted as functions of polystyrene equivalent molecular weight, which is the molecular weight of polystyrene which has the same hydrodynamic volume as the sample; it is emphasized that this is not the actual molecular weight of the sample. The data show a minor electronic acquisition problem seen as discontinuities at M sty eq 3.5 -4.

RAFT Polymerization of isoprene and butadiene in solution

	C, and total reaction time of 47 h (run VS211_68 (1)) and 95 h (run VS211_68 (2)). The
	conversions of the samples were obtained by gravimetry.
	Solution polymerization of butadiene in toluene was performed using the RAFT agent and
	AIBN. Polymerization was carried out at 60 °C in a Mettler RC1e reactor operating in batch
	mode, for 20 h.	Styrene and n-butyl acrylate (Sigma Aldrich) were purified by
	passing the monomer through an inhibitor removal column (Sigma Aldrich) twice to remove
	inhibitor and other impurities. Isoprene (Aldrich, 99%) was filtered under vacuum though 0.2
	µm Teflon filter and then passed through a column to remove inhibitor. The inhibitor removal
	columns were Aldrich Catalog No. 31,134-0 for removing t-butylcatechol from isoprene and
	31,133-2 for removing hydroquinone from styrene. An ice bath was kept at the collection
	point to prevent evaporation of isoprene. The absence of the polymer was checked by
	subjecting the pure monomer to size-exclusion chromatography (SEC) in tetrahydrofuran
	(HPLC Grade) as eluent. In some instances, if the isoprene monomer was not filtered, only a
	few drops of isoprene were collected after the inhibitor removal column, and non-filtered
	isoprene exhibited two peaks in SEC for both monomer and polymer. The polymer peak
	corresponds to very high molecular weights, > 5 ×10 6 g.mol -1 polystyrene equivalent. The
	polymer peak was absent after filtration. Butadiene was kindly supplied by RLA Polymers
	and this gaseous monomer was used without further purification.
	The RAFT agent, 2-[(dodecylsulfanyl)carbonothioyl]sulfanyl propanoic acid, was kindly
	supplied by Dulux Australia; its purity was checked by NMR (see Supporting Information).
	The initiator for emulsion polymerizations was 4,4 -azobis(4-cyanopentanoic acid) (V-501,
	Wako Industries). 1,4-dioxane (Aldrich, >99%) was distilled and kept under a nitrogen
	atmosphere. The initiator for solution polymerizations was AIBN (azobisisobutyronitrile,
	from Sigma-Aldrich, recrystallized from hexane prior to use)
	Isoprene polymerization in solution (dioxane) was performed by chain growth starting with
	AA 10 -St 12 -RAFT using a ratio of monomer: RAFT: initiator of 100: 1: 0.2, temperature 60
		page 7

  AIBN) ratio of 500: 1: 0.5 at 60 ºC over 95 h. The same ratios were applied in this work under the same conditions except that the chain transfer agent was the C 12 -RAFT agent used by Ferguson et al. instead of ETSPE, and the polymerization is here performed in dioxane or propylene glycol solution instead of bulk. The two RAFT agents have similar structure (Figure

					has been shown to be effective for controlled
	radical polymerization of styrene, n-butyl acrylate and other monomers in emulsion, using 2-
	[dodecylsulfanyl)carbonothioyl]sulfanyl propanoic acid (C 12 -RAFT) as RAFT agent. To
	apply this process to isoprene and butadiene, it is necessary to test the reactivity of this RAFT
	agent toward these dienes. Jitchum and Perrier [32] showed a control of polystyrene-
	equivalent	molecular	weight	of	isoprene	polymerization	using	2-

ethylsulfanylthiocarbonylsulfanyl-propionoic acid ethyl ester (ETSPE), with an isoprene: page 11 RAFT agent : initiator (

Table 1 :

 1 Polymerizations targetting isoprene Temperature 60 ºC, initiator V501 with a ratio of RAFT:initiator of 1:0.5, 40 units of isoprene were added for the polymerization process. This reaction was carried out under reflux to avoid loss of isoprene through heating. The product was soluble in THF + TFA.

	'I' = isoprene; 'St' = styrene, 'AA' = acrylic acid
	Experiment	Precursor	Targetted final	Solution	Reactor type and charge	Targetted	polymerization	Conversion
			polymer	or			final solid	time (h)	(%)
				emulsion			fraction
							(%)
	GB237-19	AA,RAFT	AA 10 -RAFT	solution Flask	48	3.5 h (70 ˚C)	-
	GB237-024	AA 10 -RAFT	AA 10 -(St 38 -	emulsion Flask, fed with syringe pump. 5 wt% n-	10	3 h (70 ˚C)	86
			random-BA 2 )-		butyl acrylate was added to the styrene
			RAFT
	GB237-033	AA, RAFT	AA 10 -RAFT	solution Flask. No feed -batch reaction	44	3 h (70 ˚C)	91
	GB237-034	AA 10 -RAFT	AA 10 -St 5 -	solution Flask. No feed -batch reaction	35	3 h (70 ˚C)	77
		(GB237-33)	RAFT
	GB237-035	AA 10 -St 5 -	AA 10 -St 45 -	emulsion RC1e, begin feed at rate 5 g/h for 1 h,	10	12 h, (70 ˚C)	55
		RAFT (GB237-	RAFT		then rate of 16 g/h for 1 h, then 10 h at
		34)			70	˚C
	GB237_36	AA 10 -St 45 -	AA 10 -St 45 -I 50 -	emulsion RC1e fed with pump	10	10	58
		RAFT (GB237-	RAFT
		35)
	VS211_23	AA, RAFT	AA 10 -RAFT	solution Flask	40	3
	VSS211_24	AA 10 -RAFT	AA 10 -St 12 -	solution AA 10 -St 12 -RAFT	74	Overnight , 70	85
		(VS211_23)	RAFT					˚C
	VS211_25b	AA 10 -St 12 -	AA 10 -St 12 -I 36 -	emulsion RC1e Batch mode	7.4	10 (70/115 ˚C) 50
		RAFT	RAFT
		(VS211_24)
	VS211_30	AA, RAFT	AA 10 -RAFT	solution Flask	40	3 h (70 ˚C)	95
	VS211_31	AA 10 -RAFT	AA 10 -St 12 -	solution Flask	40	Overnight , 70	60
		(VS211_30)	RAFT					˚C
	VS211_32	AA 10 -St 12 -	AA 10 -St 12 -I 36 -emulsion RC1e Batch mode	7.3	2 h (70/115	27

*

Table 2 .

 2 Polymerizations targetting butadiene. Initiator: AIBN for solution polymerization, V-501 for emulsion polymerization. 60 ˚C.

	'Bu' = butadiene; 'BA' = butyl acrylate; 'St' = styrene
	Experiment	Precursor	Targetted final	Solution	Reactor type and charge	Targetted	polymerization time Conversion
			polymer	or		final solid		(%)
				emulsion		fraction (%)
	RH_50	RAFT	Bu 377 -RAFT	solution RC1e ; Bu in toluene,	21	20 h	5
					monomer fed over 20 h
	RH_45	1. AA 10 -BA 15 -	AA 10 -BA 25 -	emulsion RC1e ; 5.4 mM V-501	9.9	25 min
		RAFT (in	RAFT
		propylene
		glycol)
		2.	AA 10 -BA 25 -		2.9 mM V-501	9.9	3 h	92
			St 15 RAFT
		3.	AA 10 -BA 25 -		3.3 mM V-501	15.0	12 h	96
			St 150 -Bu 250 -
			RAFT

Table 3 .

 3 Particle size data for isoprene and butadiene polymers. Structures of the RAFT agent used in this study, 2-[(dodecylsulfanyl)carbonothioyl]sulfanyl propanoic acid, and of the RAFT agent previously used successfully for RAFT-controlled isoprene polymerization in solution, 2-ethylsulfanylthiocarbonylsulfanylpropanoic acid ethyl ester

	'I' = isoprene; 'St' = styrene, 'AA' = acrylic acid; Bu = butadiene
	Experiment	Targetted composition	Experimental z-average radius	Expected number-averaged radius after isoprene
			(nm)	polymerization (conversion)
	VS211_24	AA 10 -St 12-RAFT	7.0	-
	VS211_25	AA 10 -St 12 -I 36 -RAFT	16.2	9.15 (85%)
	VS211_31	AA 10 -St 12 -RAFT	8.0	-
	VS211_32	AA 10 -St 12 -I 36 -RAFT	7.5	10.0 (60%)
	VS211_35	AA 10 -St 12 -RAFT	7.2	-
	VS211_36	AA 10 -St 12 -I 36 -RAFT	11.8	-
	VS211_65	AA 10 -St 12 -RAFT	6.1	-
	VS211_66	AA 10 -St 12 -I 36 -RAFT	8.5	7.1 (66%)
	RH_45	AA 10 -BA 25 -St 150 -Bu 250 -	47 ( calculated z-average from
		RAFT	experimental PSD = 39 nm)

Figures Figure 1.

ACKNOWLEDGEMENTS

We gratefully acknowledge the financial support of Ansell Sdn. Bhd. and of a Linkage grant from the Australian Research Council. The help of Chris Such and Algy Serelis of Dulux Australia for a gift of the RAFT agent is much appreciated, as is the supply of butadiene by Steve Etches of RLA Polymers. Useful discussions and advice on RAFT polymerization from Prof Sébastien Perrier, Dr Ewan Sprong, Dr Desi Ganeva, Dr Binh TT Pham and Dr Brian page 22 Hawkett are gratefully acknowledged, as is the participation of Lior Bar-Nes for the RC1e set-up and Dr Hank de Bruyn for particle size measurements. MG would like to thank the Centre for Magnetic Resonance of the University of Queensland for the use of the solid-state NMR spectrometer. page 23