high-performance PEs are fabricated via facile thiol-Michael addition catalyzed by triethylamine in the presence of lithium salts. The lithium salt functions as both ion source and co-catalyst, significantly accelerating the thiol-Michael addition reaction.

The PEs exhibits a superior thermal decomposition temperature up to 300 o C.

Additionally, PEs from the thiol-decorated polyhedral oligomeric silsesquioxane display reversible electrochemical response and stable cycling performance. Our finding based on a self-catalyzed strategy provides a promising direction for rapidly fabricating PEs that meet electrochemical requirements for practical solid polymer batteries.

INTRODUCTION

The increasing demand for electric vehicles and efficient energy storage devices promotes the development of rechargeable batteries with high energy density and long cycle life. [START_REF] Armand | Building Better Batteries[END_REF][START_REF] Kang | Battery Materials for Ultrafast Charging and Discharging[END_REF][START_REF] Aricò | Nanostructured Materials for Advanced Energy Conversion and Storage Devices[END_REF][START_REF] Winter | Before Li Ion Batteries[END_REF][START_REF] Cao | Bridging the Academic and Industrial Metrics for Next-Generation Practical Batteries[END_REF][START_REF] Goodenough | The Li-Ion Rechargeable Battery: A Perspective[END_REF] However, lithium-ion batteries (LIBs) with liquid organic electrolytes have brought security and reliability concerns owing to inherent limitations such as high volatility, leaks, and explosions. [START_REF] Tarascon | Issues and Challenges Facing Rechargeable Lithium Batteries[END_REF][START_REF] Hammami | Lithium-Ion Batteries: Runaway Risk of Forming Toxic Compounds[END_REF] It is thus expected that replacing conventional liquid organic electrolytes with polymer electrolytes (PEs) can improve the Li-based battery safety, performance, and machinability. [START_REF] Lopez | Designing Polymers for Advanced Battery Chemistries[END_REF][START_REF] Zhou | Polymer Electrolytes for Lithium-Based Batteries: Advances and Prospects[END_REF][START_REF] Manthiram | Lithium Battery Chemistries Enabled by Solid-State Electrolytes[END_REF][START_REF] Miller | Designing Polymer Electrolytes for Safe and High Capacity Rechargeable Lithium Batteries[END_REF] The poly(ethylene oxide) (PEO) has been most widely studied for PE systems because of its high dielectric constant and ability to form complex with lithium salts. [START_REF] Xue | Poly(ethylene oxide)-Based Electrolytes for Lithium-Ion Batteries[END_REF][START_REF] Xu | High-Performance All-Solid-State Batteries Enabled by Salt Bonding to Perovskite in Poly(ethylene oxide)[END_REF] Nevertheless, lithium-salt doped PEO exhibits low ionic conductivity at room temperature originating from its semi-crystalline nature, which hampers the transport of lithium ions through the polymer chain segments. [START_REF] Croce | Nanocomposite Polymer Electrolytes for Lithium Batteries[END_REF] Building a cross-linked framework [START_REF] Zeng | Reshaping Lithium Plating/Stripping Behavior via Bifunctional Polymer Electrolyte for Room-Temperature Solid Li Metal Batteries[END_REF][START_REF] Choudhury | A Highly Reversible Room-Temperature Lithium Metal Battery Based on Crosslinked Hairy Nanoparticles[END_REF][START_REF] Choudhury | Solid-State Polymer Electrolytes for High-Performance Lithium Metal Batteries[END_REF][START_REF] Lu | Dendrite-Free, High-Rate, Long-Life Lithium Metal Batteries with A 3D Cross-Linked Network Polymer Electrolyte[END_REF][START_REF] Yu | Monochromatic "Photoinitibitor"-Mediated Holographic Photopolymer Electrolytes for Lithium-Ion Batteries[END_REF][START_REF] Zuo | Cyclophosphazene-Based Hybrid Polymer Electrolytes Obtained via Epoxy-Amine Reaction for High-Performance All-Solid-State Lithium-Ion Batteries[END_REF] or loading inorganic components into the polymer matrices [START_REF] Lin | A Silica-Aerogel-Reinforced Composite Polymer Electrolyte with High Ionic Conductivity and High Modulus[END_REF][START_REF] Wan | Ultrathin, Flexible, Solid Polymer Composite Electrolyte Enabled with Aligned Nanoporous Host for Lithium Batteries[END_REF][START_REF] Gao | Polymer-Inorganic Solid-Electrolyte Interphase for Stable Lithium Metal Batteries under Lean Electrolyte Conditions[END_REF][START_REF] Lin | High Ionic Conductivity of Composite Solid Polymer Electrolyte via In Situ Synthesis of Monodispersed SiO2 Nanospheres in Poly(ethylene oxide)[END_REF][START_REF] Pan | Hybrid Electrolytes with Controlled Network Structures for Lithium Metal Batteries[END_REF][START_REF] Zhou | Self-Healing Composite Polymer Electrolyte Formed via Supramolecular Networks for High-Performance Lithium-Ion Batteries[END_REF][START_REF] Hu | Poly(ethylene oxide)-Based Composite Polymer Electrolytes Embedding with Ionic Bond Modified Nanoparticles for All-Solid-State Lithium-Ion Battery[END_REF] can efficiently improve ionic conductivity by inhibiting the crystallization and simultaneously enhance the mechanical properties of the PEs.

The thiol-ene reaction can generally proceed via either radical-mediated anti-Markovnikov addition or base-or nucleophile-catalyzed thiol-Michael addition. [START_REF] Mather | Michael Addition Reactions in Macromolecular Design for Emerging Technologies[END_REF][START_REF] Hoyle | Thiol-Click Chemistry: A Multifaceted Toolbox for Small Molecule and Polymer Synthesis[END_REF][START_REF] Nair | The Thiol-Michael Addition Click Reaction: A Powerful and Widely Used Tool in Materials Chemistry[END_REF] Owing to the rapid reaction kinetics, high efficiency, chemo-selectivity, and benign reaction conditions, the thiol-ene reaction has become a particularly useful tool in polymer chemistry and materials science, [START_REF] Tasdelen | Externally Stimulated Click Reactions for Macromolecular Syntheses[END_REF][START_REF] Worrell | Bistable and Photoswitchable States of Matter[END_REF][START_REF] Chatani | Facile and Efficient Synthesis of Dendrimers and One-Pot Preparation of Dendritic-Linear Polymer Conjugates via a Single Chemistry: Utilization of Kinetically Selective Thiol-Michael Addition Reactions[END_REF][START_REF] Hu | Flexible Organic-Inorganic Hybrid Solid Electrolytes Formed via Thiol-Acrylate Photopolymerization[END_REF][START_REF] Hong | Tailored CO2-philic Gas Separation Membranes via One-Pot Thiol-ene Chemistry[END_REF] including polymer network construction, surface functionalization and dendrimer synthesis. For instance, Saito et al. [START_REF] Hong | Tailored CO2-philic Gas Separation Membranes via One-Pot Thiol-ene Chemistry[END_REF] synthesized poly(dimethylsiloxane)-poly(ethylene glycol) methyl ether acrylate (PDMS-PEGMEA)-based co-polymer membranes via UV initiated one-pot thiol-ene reaction to fabricate elastic polymer materials used for gas separation application. Fang et al. [START_REF] Fang | Phosphorus-and Sulfur-Containing High-Refractive-Index Polymers with High Tg and Transparency Derived from a Bio-Based Aldehyde[END_REF] used thiol-ene reaction to prepare two flexible and colorless phosphorous-sulfide polymer films based on a phosphorus-containing derivative of aromatic aldehyde (4hydroxybenaldehyde). Grewal et al. [START_REF] Grewal | Bifunctional Poly(ethylene glycol) Based Crosslinked Network Polymers as Electrolytes for All-Solid-State Lithium Ion Batteries[END_REF] and Suk et al. [START_REF] Suk | Semi-Interpenetrating Solid Polymer Electrolyte Based on Thiol-Ene Cross-Linker for All-Solid-State Lithium Batteries[END_REF] reported polymer electrolytes based on a crosslinked network formed via thiol-ene reaction using a thermal initiator.

However, it is difficult to obtain an ideal 1:1 stoichiometric reactivity through conventional free radical-mediated addition, which means the simultaneous existence of thiol-ene and ene-ene reaction will most probably pose difficulties for the acquisition of well-defined polymer structure. [START_REF] Zhong | Tailorable, 3D Structured and Micro-Patternable Ionogels for Flexible and Stretchable Electrochemical Devices[END_REF] To tackle this problem, several approaches are proposed by researchers. Bowman and co-workers [START_REF] Xi | Spatial and Temporal Control of Thiol-Michael Addition via Photocaged Superbase in Photopatterning and Two-Stage Polymer Networks Formation[END_REF][START_REF] Zhang | o-Nitrobenzyl-Based Photobase Generators: Efficient Photoinitiators for Visible-Light Induced Thiol-Michael Addition Photopolymerization[END_REF][START_REF] Huang | Mechanistic Modeling of the Thiol-Michael Addition Polymerization Kinetics: Structural Effects of the Thiol And Vinyl Monomers[END_REF] synthesized visible-lightsensitive photo-base generators applied in thiol-Michael addition reactions, which allows a stoichiometric reaction of both thiol and vinyl functional groups and enables homogeneous network formation. Photopolymerization, as well as the introduction of allyl groups, has been an effective method to develop a controlled network through precise design of the polymer structure, but the complicated synthesis and severe operation condition limit the practical application. Thus, a convenient fabrication process is necessary to form PEs with improved ionic conductivity, high thermal stability, and excellent cycling performance, which can be achieved by using thiol-Michael addition. Thiol-Michael addition is modular in nature, highly efficient, and exhibits stoichiometric reactivity of 1:1, hence classified as a "click" reaction. By the adjunction of minimal dosage of catalysts (base or nucleophilic reagent) under ambient temperature, it can occur without any exposure to heat or light. In recent years, the thiol-Michael addition bas been employed in a large extent of applications, such as small molecule synthesis, surface functionalization, bioconjugation, tissue engineering, dendrimer synthesis, and polymer network synthesis. [START_REF] Tasdelen | Externally Stimulated Click Reactions for Macromolecular Syntheses[END_REF] The self-catalyzed strategy is an attractive method to fabricate PEs via a simple preparation routine with the lithium salts employed as ion sources on one hand and as catalysts on the other hand. In 2001, Tsutsumi and co-workers [START_REF] Miwa | Polymerization of Bis-Oxetanes Consisting of Oligo-Ethylene Oxide Chain with Lithium Salts as Initiators[END_REF] reported that various lithium salts could initiate the cationic ring-opening polymerization (ROP) of bisoxetanes, indicating the potential of self-catalyzed strategy in polymer electrolyte field.

Cui et al. [START_REF] Cui | High Performance Solid Polymer Electrolytes for Rechargeable Batteries: A Self-Catalyzed Strategy Toward Facile Synthesis[END_REF] reported a crosslinked PE by a self-catalyzed strategy and in-situ technology via a facile cationic polymerization initiated by lithium salts. Recently, Li et al. [START_REF] Liu | Upgrading Traditional Liquid Electrolyte via In Situ Gelation for Future Lithium Metal Batteries[END_REF]

used

LiPF6 to induce the cationic polymerization of the ether-based 1,3-dioxolane and 1,2-dimethoxyethane liquid electrolyte and fabricated quasi-solid gel PEs. Archer et al. [START_REF] Zhao | Solid-State Polymer Electrolytes with In-Built Fast Interfacial Transport for Secondary Lithium Batteries[END_REF] reported cationic aluminum species-initiated ROP of 1,3-dioxolane inside an electrochemical cell to produce PEs. The self-catalyzed strategy offers incomparable advantages including facile preparation procedure, efficiency, high production and low costs. Yet, the uncontrollability of chain-growth polymerization is hardly satisfactory if the formation of a well-defined polymer electrolyte network is desired. More importantly, compared with electrolytes formed via the self-catalyzed strategy, which are neat polymer matrices, preparing composite polymer electrolytes with inorganic nanofillers introduced is an effective strategy to enhance the ionic conductivity and cycling stability of LIBs. Several studies on organic-inorganic hybrid polymer electrolytes have certificated the mechanism of ionic conductivity enhancement, the interactions between polymer matrix and inorganic fillers at the interface. [START_REF] Dirican | Composite Solid Electrolytes for All-Solid-State Lithium Batteries[END_REF] First, due to chemical or/and physical interactions, polymer segments can be attracted by the surface sites of ceramic fillers, providing amorphous-rich areas as Li + transport channels near surface region of inorganic fillers. Second, there are intense interaction between anionic groups of lithium salts and chemical groups of ceramic fillers, promoting the lithium salts dissociation and leading to the increase of free Li + concentration at the interface. Third, the interaction between polymer chains and inorganic fillers could influence the local conformation of segments in polymer, which probably provides Li + -conductive substructures for polymer matrix. Moreover, compared with neat polymer matrix, the cycle stability of composite polymer electrolytes could be improved because the mechanical strength inorganic fillers provided is helpful to prevent the growth of lithium dendrites. [START_REF] Xia | High-Rate and Large-Capacity Lithium Metal Anode Enabled by Volume Conformal and Self-Healable Composite Polymer Electrolyte[END_REF] Cui et al. [START_REF] Zhang | Vertically Aligned and Continuous Nanoscale Ceramic-Polymer Interfaces in Composite Solid Polymer Electrolytes for Enhanced Ionic Conductivity[END_REF] reported a composite polymer electrolyte with vertically aligned ceramic-polymer interfaces, achieving high interfacial ionic conductivity and long cycle life when compared to the PE without nanofillers.

Herein, we applied the thiol-Michael addition as a platform to fabricate crosslinked electrolytes with well-defined network by employing a selection of multifunctional thiols, poly(ethylene glycol) diacrylate (PEGDA, Mn = 200, 400, or 600)

with triethylamine (TEA) as a catalyst in the presence of lithium salts (Figure 1).

Studies on the polymerization kinetics denote that lithium salts (lithium perchlorate, lithium bis(trifluoromethanesulfonyl)imide and lithium trifluoromethanesulfonate) are capable of significantly accelerating the base-catalyzed thiol-Michael addition, which enables them to act as ion sources as well as co-catalysts in the polymerization.

Moreover, some other alkali metal salts including sodium perchlorate and potassium perchlorate have also shown the same effect as the lithium salts. The novel selfcatalyzed strategy for the base-catalyzed one-pot thiol-Michael addition reaction under ambient temperature described in the present work provides a facile fabricating procedure of PEs. Furthermore, we introduce the thiol-decorated polyhedral oligomeric silsesquioxane (POSS-SH, Figure S1, Supporting Information) into electrolyte networks, which plays an important role in promoting the thermal performance and decreasing the crystallinity of PEs because of the intramolecular organic-inorganic hybrid structure. Moreover, the ideal 1:1 stoichiometric reactivity of thiol group and acrylate group will be conducive to the uniform dispersion of POSS and effectively avoid agglomeration of nano-particles, which can lead to negative impact on polymer electrolytes, including growth of lithium dendrite, poor interfacial contact between electrode and polymer electrolytes, and increase of interfacial impedance. As a result of the cross-linked structure and presence of the inorganic component, the ionic conductivity and mechanical property of PEs are also enhanced. The constructed LIBs on the basis of these PEs as separators, lithium iron phosphate (LFP) as cathode and lithium metal as anode show impressive electrochemical performances including a stabilized plating/stripping process and promising cycling property. DFT Calculations. The computational work was carried out using the Gaussian09 suite of programs. [START_REF] Frisch | Revision D.01[END_REF] Gas-phase geometry optimizations were performed without any symmetry constraint using the B3LYP functional and the 6-31G(d,p) basis functions for all atoms. Dispersion interactions were taken into account by Grimme's D3 empirical method during the geometry optimizations (B3LYP-D3). [START_REF] Grimme | A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu[END_REF] All final geometries were characterized as stationary points by verifying that all second derivatives of the energy were positive. Thermochemical corrections were obtained at 298.15 K on the basis of frequency calculations, using the standard approximations (ideal gas, rigid rotor and harmonic oscillator). A solvation correction was carried out on the gas-phase optimized molecules by fixed-geometry calculations in the presence of a polarizable continuum with the Gaussian09 library values for the permittivity of chloroform (ε = 4.7113) or THF (ε = 7.4257). A further correction of 1.95 kcal mol -1 was applied to bring the G values from the gas phase (1 atm) to the solution (1 mol L -1 ) standard state. [START_REF] Bryantsev | Calculation of Solvation Free Energies of Charged Solutes Using Mixed Cluster/Continuum Models[END_REF] The NMR spectra in chloroform solution were calculated by the Gaussian09 package using the standard Gauge-Independent Atomic Orbital (GIAO) method. [START_REF] Wolinski | Efficient Implementation of the Gauge-Independent Atomic Orbital Method for NMR Chemical Shift Calculations[END_REF] and of the PEGDA600 vinyl moiety at 1630 cm -1 fade away after the thiol-Michael addition (Figure S4), confirming that the PEGDA600 and multifunctional thiols monomers have reacted completely. The uniform distribution of carbon, oxygen, silicon, and sulfur elements, shown by the energy dispersive X-ray (EDX) analysis of crosssection (Figure 2b), suggests that no significant inorganic nanoparticles aggregation occurs (the original SEM image is shown in Figure S5). This good dispersibility of inorganic fillers is beneficial for the improvement of the mechanical properties. The real-time FT-IR spectroscopy was also employed to reveal the reaction kinetics of the TEA-catalyzed thiol-Michael addition using PEGDA200 and 1hexanethiol (HT) as model substrates by monitoring the disappearance of acrylate and thiol peaks (Figure S6). In the absence of LiClO4, this addition reaction proceeded slowly, reaching only about 3% conversion of both vinyl and thiol groups in 30 min, whereas the reaction proceeds to nearly full conversion in 30 min in the presence of the salt (Figures 3a and3b). The kinetics of the reaction does not strongly depend on the PEGDA200:LiClO4 ratio (Figure S7). Figure S8 shows that no significant conversion of the thiol and vinyl groups for the mixture of PEGDA200 and HT takes place after 1 h in the absence of TEA, even if LiClO4 is present (PEGDA200 : LiClO4 = 20:1). This result clearly establishes that both TEA and LiClO4 are essential to accelerate the reaction. The time-conversion curves for the reactions carried out in the presence of a few other alkali metal salts, including LiTFSI, LiCF3SO3, NaClO4, and KClO4 (Figures 3a and3b) illustrate that they also function as co-catalysts, especially LiTFSI, LiCF3SO3 and NaClO4. DFT Calculations and Mechanistic Aspects. It is known that the double bond conjugation in acrylate substrates renders the vinyl group electron deficient and therefore suitable for the thiol-Michael addition because the nucleophilic attack by a thiolate anion is accelerated. In addition, stronger electron withdrawing groups should lead to greater electron deficiency and therefore to higher reactivity. We can imagine that coordination of Li + to the oxygen from carbonyl moiety of the acrylate group decreases the vinyl group electron density, thus leading to a faster reaction. To evaluate this hypothesis, we tested the interaction between different salts and the acrylate group by [START_REF] Armand | Building Better Batteries[END_REF] H NMR spectroscopy in CDCl3 (Figure 3c), where all salts were fully dissolved.

RESULT AND DISCUSSION

In comparison with pure PEGDA600, the methylene proton signals of the PEGDA600/LiClO4 mixture shift to lower field, suggesting a decreased electron density for the vinyl group. The resonance shifts are greater for greater LiClO4 to PEGDA600 ratios (Figure S9a). The resonance shift is also evident for the other lithium salts, particularly for LiTFSI where the larger anion may favor a stronger salt dissociation, and also for NaClO4, whereas KClO4 has a negligible effect. The position of methylene proton signals also remains essentially unchanged when PEGDA600 is mixed with TEA only (Figure S9c), indicating that TEA does not have the same effect of decreasing the vinyl electron density.

The above hypotheses were also supported by density-functional theory (DFT) calculations, which provided, in addition, an insight into the reaction mechanism. The effect of the salt interaction with the acrylate function was probed by performing calculations on adducts of methyl acrylate, as a model substrate, with MtClO4 (Mt = Li, Na, K) in the presence of a polarizable continuum to model the chloroform solvent. Full details are provided in the Supporting Information. Since chloroform has poor coordinating properties, the salt was introduced in the calculation without explicit solvent molecules. In addition to showing a favorable interaction in the order Li > Na > K (ΔGD3,298K,CHCl3 = -19.1, -15.7 and -10.8 kcal mol -1 , respectively), the calculations predict that the O•••Mt interaction lengthens the O=C bond and slightly shortens the (O)C-C bond, whereas the vinyl C=C bond remains practically unaltered, while increasing the Mulliken charge on all three vinyl H atoms (details in Table S1). These effects are again decreasing in the order Li > Na > K. Finally, the calculations predict a downfield shift of the 1 H NMR resonance for all three vinyl H atoms, relative to free MA, in agreement with the experimental trend (Table S1).

The The initial addition of Mt + (SMe -) to MA is exoergic in the order Li > Na > K. Placing these pathways on the same scale relative to MA (plus MeSH, NEt3 and Mt + ClO4 -) requires however assessment of the ion metathesis between Mt + ClO4 -and Et3NH + MeS -.

This was probed using again the naked cation, yielding the results shown in Figures S13-S15. The most interesting result is that the ion metathesis is quite favorable, thus the proton transfer from MeSH to NEt3 in the presence of Mt + ClO4 -(leading to MtSMe + Et3NH + ClO4 -) is less energetically costly than in the absence of salt. These results

should not be considered as quantitatively reliable, because of the unrealistic model with neglect of solvent coordination to the alkali cation. Another drastic approximation is the neglect of the ion pair dissociation to the free ions. This dissociation likely becomes more favorable for the larger cations (K > Na > Li), thus the energetic cost of the initial proton transfer, which also reflects onto the energy of the rate-determining transition state, is probably greater than what is shown in Figures S13-S15, approaching the energetic cost calculated in the absence of salt in Figure S10. In spite of all these approximations, the study qualitatively suggests that the reaction is accelerated, because the energy needed to bring together the anionic nucleophile and the substrate is lowered, which is owing to the more favorable ion pairing in the Et3NH + ClO4 -and Mt + SMe -salts than in the metathesized pair (Mt + ClO4 -and Et3NH + SMe -). segments leads to slower chain relaxation, higher Tg, which is to the disadvantage of improvement of ionic conductivity. [START_REF] Duan | In-Situ Plasticized Polymer Electrolyte with Double-Network for Flexible Solid-State Lithium-Metal Batteries[END_REF] Tg decreases with an increase of the PEGDA molecular weight, as shown by the different scanning calorimetry (DSC) analyses (Figure 5 and Table S3), because longer PEGDA chains are capable of promoting the molecular relaxation of the PEs. Besides, the Tg values of PEGDA600-TMPTMP (TMPTMP refers to trimethylolpropane tris(3-mercaptopropionate)) and PEGDA600-PETMP are also lower. The toughness of PEs is important to restrain growth of lithium dendrite and prevent from penetration, which can be characterized by tensile test. In general, tensile stress is utilized to assess intrinsic resistance for fracture of polymer materials. [START_REF] Tanaka | Determination of Fracture Energy of High Strength Double Network Hydrogels[END_REF] Thus, the tensile stress is available to estimate the resistance for fracture when lithium dendrites penetrate the PEs. [START_REF] Wu | Tough Gel Electrolyte Using Double Polymer Network Design for the Safe, Stable Cycling of Lithium Metal Anode[END_REF] The tensile stress of the PEGDA600-S-POSS PE reaches 310 kPa (Figure S16), demonstrating good mechanical strength and suggesting that this PE can meet the requirements for their practical applications in LIBs. Electrochemical Performances. Generally, only the amorphous fraction of PEO is beneficial to ionic conduction because cation transport is coupled with the PEO mobility. [START_REF] Stoeva | Ionic Conductivity in the Crystalline Polymer Electrolytes PEO6:LiXF6, X = P, As, Sb[END_REF] The ionic conductivity was investigated by electrochemical impedance spectroscopy (EIS), which is a particularly important parameter to estimate the electrochemical performance of PEs. electrodes. [START_REF] Wang | High-Performance All-Solid-State Polymer Electrolyte with Controllable Conductivity Pathway Formed by Self-Assembly of Reactive Discogen and Immobilized via a Facile Photopolymerization for a Lithium-Ion Battery[END_REF] The stable interface is beneficial to reducing the solid-state interface impedance and improving the embedding/de-embedding efficiency of lithium ions on the electrode, and the cycle stability of LIBs can be thus improved. To study the potential of the PEGDA600-S-POSS PE, LIBs were assembled by combining it with LiFePO4 (LFP) as cathode and lithium metal as anode. Galvanostatic cycling measurements were conducted under 60 o C at a specific current of 0.1C to explore the cycle performance of the PE in the 2.5-4.2 V voltage range (Figure 7a).

The PE maintained a specific capacity of 146 mAh g -1 and a coulombic efficiency of 99.8% after 210 cycles. Moreover, the performance of galvanostatic cycling at 0.5C

shows little capacity decay and maintains a high coulombic efficiency (99.9%) after 200 cycles. The charge-discharge performance under a constant current (0.1C) at 60 o C is shown in Figure 7b. The charge and discharge plateaus are observed at 3.49 V and 3.38 V vs Li + /Li, respectively, demonstrating the de-intercalation and intercalation of lithium ion. The charge specific capacity is slightly higher than the discharge specific capacity. However, the difference between charge and discharge plateaus decreases as the charging/discharging process keeps going, illustrating that the reversible reaction contributes to the stabilization of the interface. Figure 7c shows the discharge profiles of Li|PEGDA600-S-POSS|LFP with charge-discharge current densities over the 0.1-1C range. A discharge capacity of 149 mAh g -1 and a coulombic efficiency of 99.8% are obtained at 0.1C. As the current density increases, the discharge capacity slightly decreased but was nevertheless maintained at relatively high levels (145 mA h g -1 at 0.2C, 134 mAh g -1 at 0.5C, and 112 mAh g -1 at 1C). The lithium battery was tested at different rates to study the durable rate capacity of the PE. The specific capacity at each current density of the Li|PEGDA600-S-POSS|LFP battery is depicted in Figure 7d.

The reversible capacity at 0.2C is 145 mAh g -1 , which is comparably high and nearly equal to the capacity of 0.1C. The reversible capacity at 0.5C and 1C is 134 mAh g -1 and 112 mAh g -1 respectively, which is approximately 90% and 75% of that at 0.1C.

More importantly, when the charge-discharge current densities returned to 0.1C, a reversible discharge capacity around 148 mAh g -1 was recovered, demonstrating that the LIBs prepared by using the PEGDA600-S-POSS PE have outstanding rate capability.

CONCLUSIONS

As evidenced above, well-defined cross-linked polymer electrolytes based on PEGDA were successfully prepared by a self-catalyzed strategy using base-catalyzed thiol-Michael addition in the presence of lithium (or other alkali metal) salts. In this reaction, the lithium salts act as ion sources and co-catalysts simultaneously. The accelerating action could be correlated with the decrease of electron density in the acrylate vinyl group caused by the interaction between the alkali metal cation and the carbonyl oxygen from acrylate group. This interaction assists the simultaneous delivery of the nucleophilic thiolate anion to the vinyl Cβ atom and of a proton from a free thiol to the Cα atom. The different equilibria between the ion pair and the free ions for the salts of different alkali metal cations seems responsible for the stronger accelerating factor exhibited for the salts of the smaller Li cation. The PEs exhibited improved ionic conductivity and thermal stability. Moreover, the Li|PEGDA600-S-POSS|LFP cells possessed stable cycling performance. This work paves the way to the development of high-performance polymer batteries via a reliable self-catalyzed strategy.

and the Analytical and Testing Center of Huazhong University of Science and Technology for use of measurement facilities.

ABSTRACT:

  Polymer electrolyte (PE) which possesses improved thermal and mechanical stability is believed by far one of the most promising electrolytes for meeting the safety and performance needs of advanced electrochemical devices. Here,

Figure 1 .

 1 Figure 1. Schematic illustration of the formation of PEs using PEGDA600 and POSS-SH catalyzed by TEA in the presence of lithium salts.

  Structure and Characterizations. FigureS3presents typical images of the ultrafast formation of a cross-linking network by PEGDA600 and pentaerythritol tetra(3mercaptopropionate) (PETMP) via TEA-catalyzed thiol-Michael addition in the presence of several types of alkali metal salts within 30 seconds at room temperature.Continuous observation of the reaction catalyzed only by TEA shows that no crosslinked network forms after 3 hours. Images of the corresponding reaction of PEGDA600 and POSS-SH are depicted in Figure2a, where 5 mL of THF was added in each experiment to guarantee full dissolution of POSS-SH. The reaction is slower than that with PETMP, but the gelification was achieved within 10 min in the presence of LiClO4 and LiTFSI, whereas the solution containing TEA only changed from the liquid to the solid state after 60 h. It is obvious that this self-catalyzed strategy via thiol-Michael addition allows the rapid construction of PEs. The Fourier transform infrared (FT-IR) analysis shows that the characteristic peaks of the POSS-SH thiol groups at 2550 cm-1

55

 55

Figure 2 .

 2 Figure 2. (a) Digital images of PEGDA600 and POSS-SH mixed with alkali metal salts. (b) EDX maps of PEGDA600-S-POSS.

Figure 3 .

 3 Figure 3. Conversion against time of vinyl (a) and thiol (b) group for the TEA-catalyzed thiol-Michael addition of PEGDA200 and 1-hexanethiol (HT). [HT] : [PEGDA200] : [TEA] = 2:1:0.043 (thiol : vinyl = 1:1) in the presence of different alkali metal salts ([PEGDA200] : [salts] = 20:1). (c) 1 H NMR spectra (CDCl3) of PEGDA600 with different alkali metal salts ([PEGDA600] : [salts] = 1:2).

  DFT calculations cannot pinpoint the role of the cation on the activation barrier for the thiol-Michael addition, because the effects of the explicit coordination of solvent molecules (THF) to the alkali cation and of ion pairing cannot be easily modelled computationally. The calculations have provided, however, useful information on the reaction mechanism, which allow the suggestion of the possible role of the cation. The reaction pathway was probed using again MA as a model substrate and MeSH as a computational model for the thiol reagent. A polarizable continuum model with the permittivity of THF, which was the reaction solvent, was used in this case. Michael additions are known to proceed by nucleophilic attack at the Cβ and yield an enolate intermediate, followed by quenching by protonation, see Scheme S1a. In the absence of base, the nucleophile (MeSH) is too weak and cannot yield the enolate intermediate. Rather, the assistance by a second MeSH molecule is necessary and the reaction proceeds by a concerted mechanism, with the simultaneous delivery of the thiolate from one MeSH molecule to Cβ and the proton from the second MeSH molecule to Cα, with a high barrier (ΔG298,THF,1M = 36.1 kcal mol -1 ). The mechanism is presented in Scheme S1b and the energy profile is shown in FigureS10.The energy barrier for the thiol addition is greatly reduced upon thiol deprotonation. The putative free enolate MeSCH2CH=C(OMe)O -product resulting from addition of the thiolate anion (MeS -) could not be obtained as a local energy minimum, converging instead to a loose MA•••SMe -adduct with a S•••Cβ contact of 2.888 Å, which is much longer than in the final MeS-CH2CH2COOMe product (1.834 Å). This adduct is destabilized relative to the sum of the reagents by 3.0 kcal mol -1 .Addition of the proton-delivering thiol molecule to the system further raises the free energy, although only slightly (3.2 kcal mol -1 ) and produces a van der Waals adduct between MA and the homoconjugate thiol-thiolate pair, [MeSH•••SMe] -, without any MeSH•••MA interaction. The nucleophilic attack is very facile, with a free energy barrier of only 6.9 kcal mol -1 relative to the sum of all reagents, to yield an intermediate, [MeSCH2CH(COOMe)] -•••HSMe, which is located at essentially the same free energy as the transition state. In this intermediate, a significant negative charge is localized on the Cα atom, which is slightly pyramidalized, and the proton delivering MeSH molecule establishes a Cα•••H-SMe interaction. Then, proton transfer to this intermediate is essentially barrierless, as shown by a relaxed scan (the transition state could not be located). Hence, the anionic addition pathway indeed occurs in a stepwise manner, but the intermediate is better described as a carbanion than as an enolate, see Scheme S1c.However, we must keep into account that the generation of the thiolate anion is thermodynamically unfavorable, because the conjugate acid of NEt3, namely the ammonium cation Et3NH + , is a stronger acid than the thiol. Indeed, a 1 H investigation of the reaction between 1-hexanethiol and NEt3 gave no evidence of proton transfer (FigureS11). The DFT calculations indicate that NEt3 and the model thiol MeSH produce an H-bonded MeS-H•••NEt3 adduct, located 0.4 kcal mol -1 higher in free energy, and the subsequent proton transfer is highly endoergic (ΔG298,THF,1M = 25.3 kcal mol -1 for the sum of the separated ions, NHEt3 + and MeS -). The NHEt3 + ••• -SMe ion pair did not yield a stable minimum, reverting back to the H-bonded adduct during the optimization. Hence, the overall barrier for the NEt3-catalyzed thiol Michael addition to acrylate is only slightly decreased (to 32.2 kcal mol -1 , see FigureS10) when also considering the cost of the thiol deprotonation.The experimental results clearly demonstrate that the presence of an alkali metal cation reduces the reaction energy span. However, the computational quantification of this effect is not straightforward because, as stated above, solvent coordination and ion pairing/free ion equilibria are not trivial to model. Optimization attempts of the intermediate enolate, MeS-CH2CH=C(OMe)(O -••• + Cat) converged in all cases to the sum of the reagents (MA•••Cat(SMe)), whether a naked metal ion (Mt + ) or a more realistic model of the solvated cation ([Mt(Me2O)3] + , with the Me2O ligands used as the computational model for THF), was used as cation. A stable local minimum could only be obtained for the anti-conformation of the Cα-Cβ bond, separating the MeS group from the cation. The MeSCH2CH=C(OMe)[OMt(Me2O)3] enolates were weakly destabilized relative to the sum of the MA and MeS[Mt(Me2O)3] reagents by about the same amount for the three cations (Li, 2.0; Na, 1.7; K, 2.1 kcal mol -1 ). Local minima could be located, however, after adding a MeSH molecule to the systems with the naked cations, which also corresponds to the addition of Mt + to the intermediate of the anionic pathway presented above. The optimized geometries of all these intermediates are comparatively shown in Figure S12. All of them show a relatively strong Mt + •••O interaction, but also feature Mt + •••S interactions involving both the free MeSH molecules and the MeS group that is already incorporated in the enolate intermediate. In addition, the Na and K systems also show an additional S-H•••Cα hydrogen bond, like in the cation-free intermediate. The reaction pathway for the thiolate Michael addition in the presence of Mt + could also be investigated starting from MA, Mt + (SMe -) and MeSH and the results are shown in Figures S13-S15. In these cases, the transition states for the final proton transfer step from MeSH to the Cα atom could be optimized, whereas those of the first step (MeS -addition to the Cβ atom) could not. All these reactions have relatively low barriers, at about the same energy relative to the sum of the three separate fragments.

Figure 4 .

 4 Figure 4. Thermogravimetric analysis (TGA) curves of PEs.

Figure 5 .

 5 Figure 5. Different scanning calorimetry (DSC) analysis of PEs.

Figure 6 .

 6 Figure 6. (a) Temperature dependence of the ionic conductivity of PEs. (b) LSV curve of PEGDA600-S-POSS at 60 o C. (c) Galvanostatic cycling performance of Li|PEGDA600-S-POSS| Li symmetric battery measured at 60 o C with current density of 0.05 mA cm -2 with capacity of 0.15 mAh cm -2 . Insets: enlarged profiles of the first 10 cycles and last 10 cycles.

  Figure6aand FigureS17show that the ionic conductivity increases with an increase of PEGDA chain length. The ionic conductivity of the PEGDA600-S-POSS with a longer PEG crosslinking chain and the controlled networks formed via the thiol-Michael reaction is 5.0 × 10 -5 S cm -1 at 30 o C and 2.3 × 10 -4 S cm -1 at 60 o C, which is far higher than that of PEGDA200-S-POSS. This is because the PEO chain segment motion depends on the ability to undergo conformational changes. The PEGDA200-S-POSS with the short PEG chain possesses the rigid crosslinked network, which is not beneficial to conducting the lithium ions effectively. The ionic conductivity results are in accordance with the Tg change shown in DSC curves, which further indicates that the controlled and flexible cross-linked PEG chain contribute to the ion conduction. Besides the polymer chain length, the inclusion of inorganic components in the polymer electrolytes is also an important avenue to influence ionic conductivity. The observed high ionic conductivity and good mechanical strength in the PEGDA600-S-POSS could be attributed to the uniform hybrid network structure. For PEs based on PEGDA600, PEGDA600-S-POSS is the one giving the highest ionic conductivity below 80 o C. At high temperatures (> 80 o C), all PEs arrive the similar conductivity, implying that polymer chains in the PEs have similar dynamics.The linear sweep voltammetry (LSV) curve of PEGDA600-S-POSS, which is sandwiched between Li metal and SS, shows a stabilized current density up to 4.5 V (Figure6b), indicating that the PEGDA600-S-POSS PE exhibits a major anodic decomposition potential at 4.5 V vs Li + /Li. This performance suggests a possible application of the PEGDA600-S-POSS in the working charge-discharge potential window between 2.5-4.2 V because there is no significant decomposition reaction in this voltage range, which is able to satisfy the demand of extensively used LiFePO4 cathode in lithium ion batteries. In addition, the LSV shows an extremely slight and broad reduction profile in the 0.7-1.4 V range, revealing that a solid electrolyte interface (SEI) layer is formed. From the chart of the AC impedance and DC polarization (FigureS18), the Li + transference number (tLi+) of PEGDA600-S-POSS at 60 o C can be calculated as 0.25. In order to explore the lithium electrodeposition in PEs, Li | PEGDA600-S-POSS | Li cells were prepared to execute galvanostatic cycling experiments at 60 o C. To evaluate the long-term cycling stability of the LIBs based on the polymer electrolytes fabricated via lithium salt-induced thiol-Michael reaction, the symmetric Li|PEGDA600-S-POSS|Li cells were prepared to execute galvanostatic cycling experiments at 60 o C. To simulate the lithium stripping/plating process, we designed a cycling procedure of three-hours for both charge and discharge with a current density of 0.05 mA cm -2 (Figure6c). The voltage-time curve is flat and stable, no decrease in the voltage and no short circuit were observed with a constant polarization for up to 1270 h, demonstrating the good compatibility between the PE and the lithium metal surface. Besides, the impedance evolution is used to evaluate the interfacial stability of the polymer electrolytes. FigureS19shows the nyquist plot of Li|PEGDA600-S-POSS|Li symmetric cell at 60 o C with varying storage time. The diameter of distorted semicircle corresponds to the interfacial resistance (Ri) of PEGDA600-S-POSS|Li. Ri decreased as the storage time increased, and stabilized after 7 days, suggesting a good interfacial stability between PEGDA600-S-POSS and Li

Figure 7 .

 7 Figure 7. (a) Cycle performance of Li|PEGDA600-S-POSS|LFP cell under galvanostatic cycling at 0.1C and 0.5C rates. (b) Charge-discharge curves at 0.1C with PEGDA600-S-POSS electrolyte showing low capacity loss and little overpotential. (c) Charge-discharge curves at 0.1C (15 mA g -1 ), 0.2C (30 mA g -1 ), 0.5C (75 mA g -1 ), and 1C (150 mA g -1 ), which respectively shows a discharge capacity of 149 mAh g -1 , 145 mA h g -1 , 134 mAh g -1 , and 112 mAh g -1 . (d) Cycling of Li| PEGDA600-S-POSS|LFP battery at 0.1C, 0.2C, 0.5C, and 1C. All experiments were conducted at 60 o C.

  Facile Fabrication of Polymer Electrolytes via Lithium Salt-Accelerated Thiol-Michael Addition for Lithium-Ion Batteries Ke Jiang, † Jirong Wang, † Cai Zuo, † Shaoqiao Li, † Sibo Li, † Dan He, † Haiyan Peng, † Xiaolin Xie, † Rinaldo Poli,* , ‡ and Zhigang Xue* , † † Key Laboratory for Material Chemistry of Energy Conversion and Storage, Ministry

of Education, School of Chemistry and Chemical Engineering, Huazhong University of Science and Technology, Wuhan 430074, P. R. China. ‡ CNRS, LCC (Laboratoire de Chimie de Coordination), Université de Toulouse, UPS, INPT, 205 Route de Narbonne, BP 44099, F-31077 Cedex 4, Toulouse, France.

For Table of Contents Use Only

ASSOCIATED CONTENT

Supporting Information

Scheme S1, Figures S1-S19, and Tables S1-S3 Corresponding Authors * E-mail zgxue@mail.hust.edu.cn (Z.X.). * E-mail rinaldo.poli@lcc-toulouse.fr (R.P.).

ORCID


est destinée au dépôt

Fluorine-18 ( 18 F) is the most favorable positon emitter for tumor imaging. However, direct 18 F-labeling of biomolecules is challenging as it involves multiple steps and stringent conditions that are generally not suitable for biomolecules whose integrity may be altered. Over the past decade, an elegant new approach has been developed by coordination of aluminum fluoride {Al-18 F}. (a) The objective of this work was to implement such a method and to find the mildest conditions compatible with heat-or acid-sensitive biomolecules. To evaluate {Al-18 F} complexation, NODA-MP-C4, a derivative of the commercially available NODA-MP-NCS, was prepared as a model compound. This model bears a thiourea function to mimic that present in the final conjugates. To guide the operational conditions in radiochemistry, a complementary study in cold series was performed.

Introduction Introduction

Materials and methods

Materials and methods

Results and discussion

Results and discussion

* Correspondence: carine.san@aphp.fr; fabienne.dioury@lecnam.net

Conclusion Conclusion

Acknowledgements

  Radiolabeling by aluminum fluoride-18 complexation: method optimization on a NODA-based model for application to sensitive biomolecule as PET tracers for oncology Carine San, Nicolas Vignal, Benoit Hosten, Marc Port, Laure Sarda-Mantel, Fabienne Dioury To cite this version: Carine San, Nicolas Vignal, Benoit Hosten, Marc Port, Laure Sarda-Mantel, et al.. Radiolabeling by aluminum fluoride-18 complexation: method optimization on a NODA-based model for application to sensitive biomolecule as PET tracers for oncology. Société de chimie Thérapeutique, 28th Young Research Fellows Meeting /Journées Jeunes Chercheurs, Feb 2021, Paris (en ligne), France. hal-On Kinetex C18 column: -Radio detection: good separation between uncomplexed {Al 18 F} + 18 F - and radiolabelled Al 18 F-L 👍 -UV detection: no separation of the different AlX-L species 👎 👉 Change for Kinetex Evo C18 (Fig 1.) Conservatoire national des Arts et métiers, HESAM Université, Laboratoire GBCM, EA 7528, 2 rue Conté, 75003 Paris (2) Université de Paris, Institut de Recherche Saint-Louis, Unité Claude Kellershohn, 1 avenue Claude Vellefaux, 75010 Paris (3) AP-HP, Hôpital Lariboisière, Médecine Nucléaire, 2 rue Ambroise-Paré, 75010 Paris (4) AP-HP, Hôpital Saint-Louis, Pharmacie, 1 avenue Claude Vellefaux, 75010 Paris

  : With financial support: ITMO Cancer of Aviesan on funds administered by Inserm, and Comité Paris de la Ligue Nationale contre le Cancer XXVIII th Young Research Fellow Meeting -11-12 th February 2021

Fig 2 .:

 2 Fig 2.: Representative radio-HPLC chromatograms of the radiolabeling reaction mixture (a: UV 254 nm, b: radio) Column: Kinetex C18 50 x 2.1 mm 2.6 µm, mobile phase: H 2 O/MeCN, gradient: 95/5 to 5/95, flow rate: 0.7 mL/min, injection volume: 5 µL

N°1 8 F activity (MBq) 18 F volume (µL) Reaction volume (µL) Reactor type * 1 or 2 pot(s) †

						Radiofluoration
							yield (%)
	1	250	50	110	Tube	2	32 %
	2	250	50	110	Tube	1	48 %
	3	500	50	110	Tube	2	22 %
	4	500	50	110	Tube	1	24 %
			Fluorine-18 transport tubing replacement
	5	250	50	110	Tube	2	87 %
	6	250	50	110	Tube	1	81 %
	7	500	50	110	Tube	2	83 %
	8	500	50	110	Tube	1	82 %
	9	500	50	110	Vial	1	75 %
	10	500	25	85	Vial	1	71 %
	11	500	25	85	Vial	1	74 %
	12	250	12.5	72.5	Vial	1	76 %
	13	250	12.5	72.5	Vial	1	79 %


Dr Yong Wang

Yajun J Zhao

Prof. Dr Shuaishuai S Zhu

Prof. Dr Xingping P Zhou
email: xpzhou@mail.hust.edu.cn

Dr Jing Xu

Xiaolin L Xie

Prof. Dr Rinaldo Poli
email: rinaldo.poli@lcc-toulouse.fr

Switchable Polymerization Triggered by Fast and Quantitative Insertion of Carbon Monoxide into Cobalt-Oxygen Bonds

A strategy that uses carbon monoxide (CO) as a molecular trigger to switch the polymerization mechanism of a cobalt Salen complex [Salen = (R,R)-N,N′-bis(3,5-di-tertbutylsalicylidene)-1,2cyclohexanediamine] from ring-opening copolymerization (ROCOP) of epoxides/anhydrides to organometallic mediated controlled radical polymerization (OMRP) of acrylates is described. The key phenomenon is a rapid and quantitative insertion of CO into the Co-O bond, allowing for in situ transformation of the ROCOP active species (Salen)Co III -OR into the OMRP photoinitiator (Salen)Co III -CO2R. The proposed mechanism, which involves CO coordination to (Salen)Co III -OR and subsequent intramolecular rearrangement via migratory insertion has been rationalized by DFT calculations. Regulated by both CO and visible light, on-demand sequence control can be achieved for the one-pot synthesis of polyester-b-polyacrylate diblock copolymers (Đ < 1.15).

Introduction

The fundamental properties and functionalities of polymers are directly correlated to their primary microstructures. Whereas enzymes display exceptional efficiency for the synthesis of precisely programmed biopolymers within a living cell, it is a major challenge to regulate polymer sequence and architecture from mixture of monomers for modern polymer chemistry. 1 An attractive solution may lay in the rapidly evolving field of switchable catalysis, whereby the reactivity of a metal-based polymerization catalyst is altered in response to an external stimulus. 2 Typically, the switch involves a change of the active species, which is achieved either via in situ modification of the metal coordination sphere through a stimulus-responsive functional group, 3 or by a metal oxidation state change via a redox process 4 . In this regard, current achievements in switchable polymerization have mostly been limited to catalysts that iterate between mechanistically similar polymerization reactions.

The ring-opening copolymerization (ROCOP) of epoxides/anhydrides has emerged as a burgeoning method to produce polyesters. 5 The wide availability of renewable monomers and the opportunity for post-polymerization modification open access to a myriad of new materials with unique properties that are not accessible through traditional condensation reactions. 6 Cobalt Salcy [bis(salicylaldimine)] complexes featuring nucleophilic axial groups [(Salcy)Co III X; X = halides, carboxyl, etc.] are among the most investigated catalysts for the copolymerization, wherein the alternative insertion of anhydrides and epoxides is directly correlated to the reversible formation and dissociation of the Co-O bonds (Scheme 1A). 7 Relative to the polar Co-O bonds, Co-C bonds tend to break homolytically to generate carbon-based radicals as is known to occur, for instance, in the biological action of vitamin B12. 8 This process may be promoted by thermal treatment or by light irradiation. 9 Recently, cobalt complexes have been used to ensure the well-controlled polymerization of a wide variety of the challenging nonconjugated monomers through the strategy known as organometallic mediated controlled radical polymerization (OMRP) (Scheme 1B). 10 Especially, Fu and Peng et al. demonstrated that an alkoxycarbonyl cobalt Salen complex (Salen is a specific Salcyl ligand with a trans-cyclohex-diyl tether, Scheme 2) could serve as the photoinitiator as well as the mediator for visible light controlled OMRP. [START_REF] Zhao | [END_REF] In order to expand the application scopes of biodegradable polymers resulted from ROCOP, intensive research efforts have been directed to the rational design and synthesis of block copolymers by combining ROCOP and other living/controlled polymerization techniques. 12 We have reported the one-step synthesis of well-defined CO2-based block copolymers via concurrent ROCOP and RAFT polymerization using a bifunctional chain transfer agent in 2018, however, only conjugated monomers such as methyl methacrylate (MMA) and styrene (St) were involved. 12b In a recent contribution, we have illustrated a mechanistic switch involving ROCOP and OMRP with a (Salen)Co system as catalyst/mediator for both mechanisms. The switch operated in the OMRP-to-ROCOP direction via a O2triggered modification of the polymer chain end from Co-R to Co-OR and was implemented for the development of diblock copolymers with a poly(vinyl acetate) block and a polycarbonate block (by ROCOP of CO2/epoxides). 2d Herein, we report a switch of polymerization mechanism in the opposite direction, from ROCOP of epoxides/anhydrides to OMRP, using carbon monoxide (CO) as a molecular trigger and the (Salen)Co III Cl complex as the mediator (Scheme 2). Central to this protocol is the direct and quantitative insertion of CO into Co-O bonds, which enables an in situ transformation of the ROCOP active species (Salen)Co III -OR into the OMRP photoinitiator (Salen)Co III -CO2R. Although CO insertions into metal-carbon single and multiple bonds are implicated in many stoichiometric and catalytic transformations of great significance in both industrial and acade-Scheme 1. Scheme 1 Chain propagation processes: cobalt(III) complex mediated ROCOP of anhydrides/epoxides (A); cobalt complex mediated controlled/ living radical polymerization of vinyl monomers (B). Scheme 2. CO-triggered switch from cobalt mediated ROCOP to OMRP for the one-pot synthesis of polyester-b-polyacrylate. mic fields, 13 those into a metal-oxygen bond are less common. 14 Most are related to the Group 10 metals and all concern metals in oxidation states up to II. In those systems, the metal-alkoxide bonds are weakened by filled-filled orbital interactions between the O lone pairs and the metal d orbitals. This process is unprecedented, to the best of our knowledge, for cobalt and for a metal complex in an oxidation state as high as III.

Results and Discussion

CO-insertion study. In our primary effort to accomplish a switch from ROCOP to OMRP, we turned for inspiration to the work of Oertling and Kadish, which described the formation of [(Porphyrin)Co III (CO)] + via binding of CO with [(Porphyrin)Co] + at room temperature. 15 The weak metal dπ→ligand π* backbonding revealed by Raman studies of the resultant [(Porphyrin)Co III (CO)] + suggests that CO is largely σ-bonded to the metal and that the carbonyl carbon atom is quite positive charged. 16 Under the assumption of a facile dissociation of (Salen)Co III -OR into [(Salen)Co III ] + and the highly nucleophilic -OR (Scheme 3A1), 17 it is possible to envision that (Salen)Co III -OR may transform into (Salen)Co III -CO2R in the presence of CO. Alternatively, CO may directly coordinate to (Salen)Co III -OR and the resulting [(Salen)Co III (CO)]OR adduct may intramolecularly rearrange via insertion (Scheme 3A2). Yet another possibility is ionic dissociation after CO coordination (Scheme 3A3). All these mechanisms were previously shown to occur for other systems, depending on the nature of the complex and on the conditions. 18 It is worth mentioning that the methoxycarbonyl cobalt complex (Salen)Co III -CO2Me used by Fu and Peng was synthesized by sequential oxidation of (Salen)Co II with oxone in methanol and carbonylation process with CO, which is indicative of the formation of a (Salen)Co III -OMe intermediate. To verify this assumption, the stoichiometric ring-opening of propylene oxide (PO) operated by (Salen)Co III Cl (complex 1) was carried out in ampule at room temperature, aiming to obtain the moisture sensitive (Salen)Co-alkoxo intermediates (2a and 2b) (Scheme 3B). 19 The reaction mixture was then allowed to stir in the dark under 1 atm CO for 12 h before removing the excess PO by evaporation under vacuum. The electrospray ionization mass spectrum (ESI-MS) of the resultant dark green powder displayed only one series of signals corresponding to [(Salen)Co III Cl+PO+CO] + (see Figure S1 in the Supporting Information), suggesting that the (Salen)cobalt-alkoxo complexes were completely converted to the targeted alkoxycarbonyl cobalt Salen complexes (3a and 3b). This green powder was also analyzed by 1 H and 13 C NMR (see Figures S2 andS3). By comparison of these spectra with those of pure 3a that was obtained following the protocol described in literature (see Figures S4 andS5), [START_REF] Zhao | [END_REF] the 3a/3b ratio could be determined as 77:23, indicative of the preferential attack on the sterically unhindered epoxide ring carbon atom during the ring opening reaction. The direct treatment of 1 with PO and 1 atm of CO also generated the alkoxycarbonyl cobalt Salen complexes, suggesting that CO does not hinder the PO ring opening on the cobalt Salen complex. The 3a/3b mixture initiated a well-controlled OMRP of methyl acrylate (MA) after an induction period of about 1 h under a light intensity of 10 mW•cm -2 . MALDI-TOF-MS spectra of the resultant poly(methyl acrylate) (PMA) exhibited two series of peaks in accordance with (Cl + PO + CO + MAn + OH)Na + and (Cl + PO + CO + MAn + OH)K + , respetively (Figure S7). This suggests that the alkoxycarbonyl cobalt Salen complexes undergo Co-acyl bond homolysis and generate alkoxycarbonyl radicals able to initiate the polymerization, which is in full agreement with the work by Fu and Peng. 11 Further experiments involving the epoxides/anhydrides ROCOP followed by the CO addition were performed to test whether each of the ROCOP active species could be effectively carbonylated (Scheme 3C). In a first experiment, the ROCOP of PO and phthalic anhydride (PA) catalyzed by 1 was conducted in the presence of a large PO excess ([PO]/[PA]/[1]=1000/100/1), ensuring the generation of the [(Salen)Co III -O-PPE] chain end (Scheme 3C1). CO was then added after a specific polymerization time. As revealed by NMR spectroscopy, the PA consumption stopped after the CO addition (see Figures S8 andS9). This suggests that CO quickly terminates the copolymerization reaction. The final product had a dark green color, consistent with the formation of a carbonyl cobalt Salen complex. The 1 H NMR and GPC analyses confirmed that the product is poly(propylene phthalate) (PPE) with complete alternation of PO and PA monomers and with a number average molecular weight (Mn) of 4.3 kg/mol and dispersity of 1.10 (see Figures S10 andS11 DFT Calculations.The remarkable and unprecedented experimental finding of a CO insertion into a Co III -alkoxide species to yield a Co III -carboalkoxy species was further investigated by DFT calculations in order to confirm its feasibility and to assess which of the three envisaged mechanisms in Scheme 3A would be preferred. Since two of the three mechanisms involve a charge separation (Scheme 3, A1 and A3), the calculations included a polarizable continuum model in propylene oxide, which was used in large excess, as solvent (ε = 16.0) and a correction for dispersion forces was also included. [START_REF] Smyth | Dielectric Behavior and Structure[END_REF] The calculations were carried out with the DFT approach at the full QM level, using slightly simplified ligands for the sake of computational efficiency.

The tBu substituents on the Salen ligand were replaced with Me groups to yield the Salen* model and the polymer chain beyond the cobalt-bonded PO unit in the polymeric -O-PPE alkoxide ligand was replaced by an H atom to yield the O-CH(Me)CH2OH alkoxide model. For other computational details, see the SI. The salient results are summarized in Figure 1. The ionic dissociation of the alkoxide to yield the [Co(Salen*)] + / -OCHMeCH2OH ion pair is energetically very costly, even in the dielectric solvent (56.8 kcal/mol). Before solvation correction, the corresponding ΔG298K,1M is 142.4 kcal/mol. Therefore, this pathway appears unfeasible. On the other hand, CO addition to the [Co(Salen*)(CO)(OCHMeCH2OH)] intermediate is relative facile. Two isomers may be obtained, the most stable of which has a trans configuration (ΔG298K,PO,1M = -7.6 kcal/mol). This isomer does not have an appropriate ligand arrangement for the migratory insertion step of pathway A2, but could lead to the ionic dissociation of pathway A3. This, however, is once again energetically too costly (ΔG298K,PO,1M = 47.4 kcal/mol). The alternative [Co(Salen*)(CO)(OCHMeCH2OH)] isomer with a cis relative arrangement of the CO and alkoxide ligands is slightly endoergic but kinetically accessible (1.4 kcal/mol), with a slightly exoenergetic bond formation (-4.2 kcal/mol) and a mild stabilization by solvation (-4.1 kcal/mol). The subsequent CO insertion is very facile, with a barrier of only 4.8 kcal/mol from the carbonyl adduct or 3.4 kcal/mol from the separated reagents, and is very exothermic. Thus, the transformation of the alkoxide into the carboalkoxyl group by CO addition is predicted to be irreversible. Calculations were also carried out to assess the

Light initiated OMRP of MA mediated by (Salen)Co III -CO2-PPE.

The (Salen)Co III -CO2-PPE product obtained from the procedure of Scheme 3C2 (Mn = 5.3 kDa, Ð = 1.15) was explored as the photoinitiator for the OMRP of MA under periodic light on-off process (Figure 2). Figure 2a reveals that visible light could give ON/OFF control over the living chain growth of PPE-b-PMA. During the whole procedure, the polymerization was wellcontrolled, as indicated by the kinetic study (Figures 2b and2c) and by the excellent match between experimental and observed molar masses. The OMRP of MA was observed to proceed with linear first-order kinetics with an induction period and an apparent polymerization rate of 5.4×10 -2 •h -1 , from which the radical concentration was estimated as ~1.11×10 -9 M. The low concentration of propagating radicals largely minimized undesirable side reactions leading to dead polymers and ensured the living character. This was expected on the basis of the previous MA polymerization study with control by (Salen)Co III -CO2-Me. [START_REF] Zhao | [END_REF] Moreover, the GPC curves of the polymeric products displayed monomodal and narrow distributions as well as a continuous molecular weight increase (Figure 2d), in agreement with the formation of PPE-b-PMA. In order to investigate the effect of light on the OMRP of MA after the induction period, comparative experiments have been conducted (i) for 4 h under a light intensity of 10 mW•cm -2 , (ii) for 1 h under a light intensity of 10 mW•cm -2 + 3 h under a light intensity of 5 mW•cm -2 , (iii) for 1 h under a light intensity of 10 mW•cm -2 + 3 h in the dark and (iv) only for 1 h under a light intensity of 10 mW•cm -2 . The conversions of MA were 28.8%, 17.6%, 14.3% and 5.4%, respectively, suggesting that the polymerization does not require constant irradiation with light, but at the same time the polymerization rate scales with the light intensity (Figures S18-S21). It is notable that the induction periods under light density of 5 mW•cm -2 and 10 mW•cm -2 are around 2 h and 1 h, respectively, indicating that stronger light density is favorable for shortening the induction periods of the OMRP mediated by the in-situ generated alkoxycarbonyl cobalt Salen complexes via CO insertion into Co-O bonds.

CO-triggered switchable polymerization from ROCOP to OMRP.

Encouraged by these results, several one-pot terpolymerizations of epoxides, anhydrides and acrylates were conducted in ampules at room temperature (Table 1). The reactions comprised three stages: 1) ROCOP of the epoxides/anhydrides mixture; 2) chain-end modification by addition of CO; 3) visible light initiated OMRP of acrylates. The ampules were kept in the dark (wrapped by aluminum foil) during steps 1 and 2. The reactions were monitored by 1 H NMR analysis of aliquots taken at regular intervals. At first, PO, PA and MA were used as the model substrates (Table 1, entries 1-5). Given that CO and visible light could provide temporal control over the ROCOP/OMRP switch and the OMRP process, respectively, it is possible to precisely manipulate the incorporation of monomers into the resulting polymer chains. Taking entry 1 as an example, ROCOP and OMRP occurred during the first stage and the third stage, respectively, as revealed by the 1 H NMR spectra (Figures S22-23). According to the NMR characterization of the isolated products, both PPE with a completely alternating PO/PA structure and PMA formed in the one-pot procedure. However, no signals corresponding to the junction units could be detected (see Figures S24-S26). Both the GPC curves of products of the first stage and the third stage exhibited monomodal and narrow distribution (Figure S27). Moreover, the theoretical molecular weights calculated from the monomer conversions were all in good agreement with the values obtained from the GPC curves. It is notable that polyester/polyacrylate ratio measured by NMR (1:2.26) agree well with that calculated from GPC analysis (1:2.29). To unambiguously verify the block structure, the 1, entry 1). The characteristic signals of both PPE and PMA blocks shared the same diffusion coefficient, whereas a blend of the PPE/PMA constituents, which were expressly synthesized by PO/PA ROCOP and by MA OMRP with approximately the same chain length ratio as the diblock copolymer, displayed two diffusion coefficients (see Figures S28 andS29). Furthermore, the quantitative insertion of CO into Co-O bonds also occurred when the CO insertion process was reduced from 12 h to 30 min (Table 1,entry 5). It is notable that, after the final OMRP stage, the PPE-b-PMA product has a (Salen)Co chain-end function linked via a Co-C bond, allowing postpolymerization modification via treatment with radical scavengers such as thiols or nitroxides. By direct addition of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) into the reaction mixture after the third stage of the reaction (Table 1, entry 2), we successfully synthesized PPE-b-PMA macromolecules end-capped with TEMPO (Scheme 4), as confirmed by 1 H NMR spectroscopy (see Figure S30), yielding an isolated polymer in the form of a white powder. The monomer scope was subsequently expanded using ethylene oxide (EO), cyclohexene anhydride (CHA), cis-5-norborneneendo-2,3-dicarboxylic anhydride (NBA), cis-1,2,3,6tetrahydrophthalic anhydride (THPA) and n-butyl acrylate (nBA) (Table 1, entries 6-10). In all cases, the targeted polyester-bpolyacrylates were successfully obtained with narrow distributions (Ð < 1.17) (see Figures S32-S62).

Conclusion

In summary, the first example of a switch from the ring-opening copolymerization (ROCOP) of epoxides/anhydrides to a lightinitiated organometallic mediated controlled radical polymerization (OMRP) of vinyl monomers has been described, using a (Salen)Co system as a common catalyst/moderating agent and CO as a molecular trigger. Central to this protocol is the direct insertion of CO into the Co-O bond of the ROCOP active species (Salen)Co III -OR to afford (Salen)Co III -CO2R, which acts as successful OMRP photoinitiator for the OMRP of MA. Mechanistic aspects concerning the quantitative transformation of the Co-O bond into a Co-CO2 bond have been reasonably proposed, as confirmed by experimental results and supported by DFT calculations. This constitutes the first example of CO insertion into a metal-alkoxide bond for cobalt and for any metal in the oxidation state III. Regulated by both CO and light, ondemand monomer incorporation has been demonstrated for the one-pot terpolymerization of epoxides, anhydrides and acrylates, allowing the elaboration of polyester-b-polyacrylate diblock copolymers with precisely programmed sequence, relative block lengths and chain-end functionality.

Experimental Section

Typical procedure for synthesis of (Salen)Co III -CO2-PPE [PPE=poly-(propylene phthalate)]. In an argon filled glove box, (Salen)Co III Cl complex (63.9 mg, 0.1 mmol), PA (1.48 g, 10 mmol) and PO (7.0 mL, 100 mmol) were charged into a 25 mL ampoule, which was wrapped in aluminum foil and equipped with a magnetic stir bar. The ampoule was taken out of the glove box and allowed to stirred at 25 o C for 24 h before it was degassed and pressurized with 1 atm CO. Then, the ampoule was allowed to stir at 25 o C for 12 h. A small aliquot of the polymerization mixture was taken out for 1 H NMR spectroscopy and the remained crude mixture was precipitated in cold n-hexane. Typical procedure for CO triggered switchable polymerization from ROCOP to OMRP. In an argon filled glove box, (Salen)Co III Cl complex (63.9 mg, 0.1 mmol), PA (1.48 g, 10 mmol), MA (9.0 mL, 100 mmol) and PO (7.0 mL, 100 mmol) were charged into a 25 mL ampoule, which was wrapped in aluminum foil and equipped with a magnetic stir bar. The ampoule was then taken out of the glove box and allowed to stirred at 25 o C. After the allotted reaction time, it was degassed and pressurized with 1 atm CO and allowed to stir at 25 o C for 12 h. Next, the aluminum foil was uncovered and the ampule was degassed and pressurized with 1 atm argon and allowed to stir at ambient temperature under irradiation of a household white LED lamp with light intensity of 10 mW•cm -2 . A small aliquot of the polymerization mixture was taken out for 1 H NMR spectroscopy and the remained crude mixture was precipitated in cold nhexane.

11

 11

Scheme 3 .

 3 Scheme 3. Mechanistic aspects concerning the CO insertion into Co-O bonds to form alkyloxy cobalt Salen complexes.

  ). The ESI-MS analysis showed two series of signals in accordance with [(Salen)Co III Cl + PO + CO + (PO + PA)n]Na + and [(Salen)Co III Cl + PO + CO + (PO + PA)n]K + , respectively (see FigureS12), indicative of the full conversion of the alkyoxy active species [(Salen)Co III -O-PPE] into (Salen)Co III -CO2-PPE. Furthermore, an isotope labeling experiment using 13 CO was conducted and the resultant polymeric product was confirmed as (Salen)Co III -C 13 O2-PPE according to the ESI-MS analysis (FigureS14), which further elucidates the mechanistic aspects related to the CO insertion process. This material was able to photoinitiate the OMRP of MA (vide infra). The comparative ROCOP experiments with excess PA (Scheme 3C2), aiming at the selective formation of a carboxyl chain end [(Salen)Co III -O2C-PPE] after full PO conversion, was executed in toluene ([PO]/[PA]/[1]/[toluene]=20/100/1/200). As for the previous experiment, CO was added at the end of the polymerization, but a white product was obtained in this case (see FiguresS15 and S16). The ESI-MS analysis of the product exhibited two series of signals, which could be assigned to [Cl + PO + (PO + PA)n + H]Na + and [Cl + PO + (PO + PA)n + H]K + , respectively (see FigureS17). Moreover, this material was not a suitable photoinitiator for the OMRP of MA. Therefore, we envision that CO can only insert into the Co-O bond of (Salen)Co III -O-PPE and not into that of (Salen)Co III -O2C-PPE. In this regard, we propose that (Salen)Co III -O2C-PPE can stoichiometrically ring-open PO in the presence of CO to generate (Salen)Co III -CO2-PPE, thus enabling the full conversion of the ROCOP active species into the carboalkoxo cobalt Salen complexes (Scheme 3C).

Figure 1 .

 1 Figure 1. Free energy profile (ΔG298K,1M) in PO (ε = 16.0) for the reaction between [Co(Salen*)(OCHMeCH2OH)] and CO to yield [Co(Salen*)(COOCHMeCH2OH)]. homolytic bond strength of the Co III -E (E = O or C) bond in the various complexes involved in this work. As a reference, the bond dissociation free energy (BDFE) of [(Salen*)Co III -CH(CH3)CO2CH3] in the PO medium at 298 K was calculated as 19. 7 kcal/mol. The Co III -O bond in [(Salen*)Co III -OCH(CH3)CH2OH] is homolytically stronger (28.1 kcal/mol), consistent with the observation that the [(Salen)Co III -O-PPE] does not initiate the OMRP of MA. Finally, the Co III -C bond in [(Salen*)Co III -CO2CH (CH3)CH2OH] is even stronger (36.7 kcal/mol). This suggests that [(Salen)Co III -CO2-PEE] produced by CO insertion will not spontaneously initiate the radical polymerization of MA under thermal activation.

  by DOSY NMR spectroscopy (Table

Figure 2 .

 2 Figure 2. Visible light initiated OMRP of MA mediated by (Salen)Co III -CO2-PPE (Mn = 5.3 kDa, Ð = 1.15) at room temperature; a household white LED lamp was used as the light source (the light intensity was 10 mW•cm -2 at the sample position). (a) Investigation of the "ON/OFF" switching regulated by light. (b) Evolution of number-average molecular weight and polydispersity (Mw/Mn) with the MA conversion; the straight line represents the theoretical mass weight evolution. (c) Kinetic plot for the OMRP of MA. (d) Evolution of the GPC traces.

Scheme 4 .

 4 Scheme 4. Postpolymerization modification of (Salen)Co terminated diblock PPE-b-PMA via treatment with TEMPO.

  Typical procedure for visible light initiated OMRP of MA mediated by (Salen)Co III -CO2-PPE. In an argon filled glove box, (Salen)Co III -CO2-PPE (Mn = 5.3 kDa, Ð = 1.15), MA were charged into a 25 mL ampoule equipped with a magnetic stir bar, [(Salen)Co III -CO2-PPE]/[MA]=1/1000, [M]0=1.0 M solvent: CH2Cl2. The ampoule was then taken out of the glove box and allowed to stirred at 25 o C under irradiation of a household white LED lamp with light intensity of 10 mW•cm -2 . A small aliquot of the polymerization mixture was taken out for 1 H NMR spectroscopy and the remained crude mixture was precipitated in cold n-hexane.

Table 1 .

 1 One-pot synthesis of block copolymers via CO triggered switchable polymerization from the ROCOP of epoxides/anhydrides to the OMRP of acrylates. a

	Entry	Monomer	Time (h)	ROCOP Conv. (%) b (anhydride)	OMRP Conv. (%) b Time (min) (acrylate)	Polyester /Polyacrylate b	Mn,theo c (kg/mol)	Mn,GPC d (kg/mol)	Ð d
	1	[PO]/[PA]/[MA]	48	31	60	17	1/2.26	21.0	20.2	1.09
	2 e	[PO]/[PA]/[MA]	60	40	10	1	1/0.10	9.1	8.2	1.13
	3	[PO]/[PA]/[MA]	72	46	50	35	1/8.73	39.5	36.7	1.25
	4	[PO]/[PA]/[MA]	72	46	90	63	1/15.7	63.5	59.6	1.23
	5 f	[PO]/[PA]/[MA]	96	58	50	16	1/1	25.8	24.6	1.13
	6	[PO]/[PA]/[nBA]	48	31	20	4	1/2.20	11.5	9.2	1.11
	7	[EO]/[PA]/[MA]	24	73	60	9	1/1.26	21.7	19.8	1.11
	8	[EO]/[CHA]/[MA]	12	23	60	33	1/4.28	33.0	30.4	1.16
	9	[EO]/[THPA]/[MA]	25	70	50	18	1/0.75	29.2	27.3	1.16
	10	[PO]/[NBA]/[MA]	65	35	40	8	1/0.60	14.6	12.7	1.15
	11	[PO]/[NBA]/[nBA]	60	29	25	2	1/0.30	9.0	7.7	1.14
	a Conditions: room temperature; [epoxide]/[anhydride]/[acrylate]/[Complex 1] = 1000/100/1000/1; CO insertion processes run for 12 h; light source for OMRP:
	household white LED lamp (10 mWcm

-2 at the sample position). b Determined by 1 H NMR spectroscopy. c Mn,theo = [Mw(epoxide) + Mw(anhydride)] × 100 × Conv.(anhydride) + Mw(acrylate) × 1000 × Conv.(acrylate). d Determined by GPC analysis in THF, calibrated against polystyrene standards. e Terminated with TEMPO. f The CO insertion process runs for 30 min.

Acknowledgements

YW, YJZ and XPZ thank the Financial support from National Key R&D Plan (No.2016YFB0302400), NSFC (No.21604027) of china, the Fundamental Research Funds for the Central Universities (HUST:2019JYCXJJ015) as well as the analytical and testing assistance from the Analysis and Testing Center of HUST. RP thanks the CNRS (Centre National de la Recherche Scientifique) for support and the CALMIP mesocenter of the University of Toulouse for the allocation of computational resources.

Conflict of interest

The authors declare no conflict of interest