Marc Guerre

RAFT synthesis of well-defined PVDF-b-PVAc block copolymers

RAFT polymerization of vinylidene fluoride (VDF), leading to relatively well defined poly(vinylidene fluoride) (PVDF), is negatively affected by chain inversion resulting in less easily reactivatable PVDFT-XA dormant chains (terminated with the tail end of an inversely added VDF unit; XA = xanthate moiety). Although slow reactivation of these chains by PVDF˙ radicals (in contrast to general belief) was recently demonstrated, slow radical exchange leads to progressive loss of chain growth control. This article deals with the possibility of synthesizing block copolymers from PVDF-XA macroCTAs by sequential addition. The investigations show that only PVDFH-XA (chains terminated with the head end of regularly added VDF) can be reactivated by PNVP˙ (poly(N-vinylpyrrolidone)) radicals and that PVDFT-XA chains are completely unreactive in the presence of PNVP˙, PB˙ (poly(butylacrylate)) or PDM˙ (poly(N,N′-dimethylacrylamide)). However, both PVDFH-XA and PVDFT-XA can be reactivated by PVAc˙ (poly(vinyl acetate)) radicals. The reactivation of the PVDFT-XA, albeit slower than that of the PVDFH-XA, is sufficiently fast to allow the synthesis of unprecedented well-defined PVDF-b-PVAc block copolymers with relatively high end-group fidelity. DFT calculations rationalize this behavior on the basis of faster radical exchange in the order PVDFH-XA/VAc > PVDFH-XA/NVP > PVDFT-XA/VAc ≫ PVDFT-XA/NVP. The success of the chain extension also relies on faster activation relative to homopropagation of the chain extending monomer, as well as fast addition of the released and to the monomer.

An amphiphilic poly(vinylidene fluoride)-b-poly(vinyl alcohol) block copolymer: synthesis and self-assembly in water

This study is the first report of the synthesis and self-assembly in water of an amphiphilic PVDF-b-PVA block copolymer. The block copolymer was prepared by sequential RAFT polymerization of VDF and VAc followed by saponification of the PVAc block and was characterized by 1H NMR and FTIR. The self-assembled nanoparticles were characterized by DLS and cryo-TEM.

Polymerization-induced self-assembly of PVAc-b-PVDF block copolymers via RAFT dispersion polymerization of vinylidene fluoride in dimethyl carbonate

Polymerization-induced self-assembly of PVAc-b-PVDF block copolymers (BCPs) in dimethyl carbonate (DMC) was performed and studied using vinylidene fluoride (VDF) RAFT dispersion polymerization protocols in DMC in the presence of PVAc macromolecular chain transfer agents (macro-CTAs). The polymerizations were conducted at 73 °C in DMC using three PVAc macro-CTAs of different molar masses and targeting various DPPVDF. The relatively high frequency of head-to-head (HH) additions in VAc polymerization and the much lower reactivity of the resulting PVAc chains terminated with a –CH(OAc)–CH2–SC(S)OCH2CH3 group (PVAcT–XA, where XA stands for the xanthate end-group) compared to their regularly terminated analogs (PVAcH–XA) leads to an accumulation of PVAcT–XA chains during polymerization. These PVAcT–XA reactivate slower than PVAcH–XA in the presence of PVDF˙ radicals. In addition, RAFT polymerization of VDF is prone to the same chain defect problem and to non-negligible transfer to DMC. In consequence, RAFT dispersion polymerization of VDF in the presence of PVAc macro-CTAs afforded PVAc-b-PVDF BCPs (contaminated with starting unreacted PVAc and PVDF homopolymers formed via transfer to DMC). These phenomena were studied using 1H and 19F NMR spectroscopy and size exclusion chromatography. Nevertheless, the VDF RAFT dispersion polymerization in DMC experiments resulted in self-assembled BCP morphologies in the form of crystalline (1–5 μm) ovoidal flakes. These flakes stack on top of each other and form star-like structures. The structures are thought to form by epitaxial growth of the PVDF crystals and interparticle interpenetration crystallization. Although they are formed under polymerization-induced self-assembly conditions, the morphologies of these BCP structures are governed by the crystallization of PVDF.

An amphiphilic PEG-b-PFPE-b-PEG triblock copolymer: synthesis by CuAAC click chemistry and self-assembly in water

A new PEG2000-b-PFPE1200-b-PEG2000 amphiphilic triblock copolymer was synthesized by copper(I)-catalyzed alkyne–azide cycloaddition (CuAAC). The microstructure of this ABA triblock copolymer was unequivocally characterized by NMR spectroscopy. Diffusion-ordered spectroscopy (DOSY) NMR experiment revealed that 1H resonances belonging to PEG and PFPE are aligned on the same horizontal line, thus implying that all these signals are due to the same macromolecule whose diffusion coefficient is lower than that of PEG and PFPE homopolymers. Thanks to its semi-fluorinated backbone bearing robust triazole rings, the PEG2000-b-PFPE1200-b-PEG2000 triblock copolymer exhibits good thermal stability with no significant weight loss until 275 °C under air. This triblock copolymer undergoes self-assembly into micelles (D = 10–20 nm) in aqueous solution as confirmed from cryogenic-temperature transmission electron microscopy, DOSY experiment in D2O, and dynamic light scattering. The critical micelle concentration was determined by pyrene fluorescence assay, and was found to be 0.1 mg mL−1.

One-pot synthesis of poly(vinylidene fluoride) methacrylate macromonomers via thia-Michael addition

This study presents a new synthetic route to prepare original PVDF macromonomers and PVDF-based architectures. A poly(vinylidene fluoride), PVDF, synthesized using MADIX controlled polymerization in the presence of O-ethyl-S-(1-methoxycarbonyl)ethyldithiocarbonate was chemically modified via two strategies and fully characterized. Using a one-pot procedure, the xanthate end-groups of the PVDF were converted into thiols which were immediately added onto the acrylate moieties of 3-(acryloyloxy)-2-hydroxypropyl methacrylate (AHPMA) via regioselective thia-Michael addition to form new PVDF-MA macromonomers. Two methods of elimination of the thiocarbonylthio group were tested and compared: aminolysis, and elimination using sodium azide. These reactions were thoroughly examined via1H and 19F NMR spectroscopy and SEC-HPLC. The aminolysis procedure was shown to give better coupling efficiency and better-defined macromonomers. The PVDF-MA macromonomers with the highest functionality were further polymerized by RAFT. The RAFT homopolymerization of PVDF-MA revealed that a non-negligible amount of macromonomers did not react. In contrast RAFT copolymerization of PVDF-MA and MMA resulted in the total conversion of the macromonomers and allowed the synthesis of novel methacrylic copolymers and block copolymers.

Synthesis of PEVE-b-P(CTFE-alt-EVE) block copolymers by sequential cationic and radical RAFT polymerization

Block copolymers containing chlorotrifluoroethylene (CTFE) are relatively rare. This article presents the synthesis of unprecedented CTFE-containing block copolymers (PEVE-b-P(CTFE-alt-EVE)), where EVE stands for ethyl vinyl ether, via sequential cationic and radical Reversible Addition–Fragmentation chain Transfer (RAFT) polymerizations. Two synthetic pathways were followed and compared: (1) synthesis of a PEVE block by cationic RAFT polymerization from a P(CTFE-alt-EVE) macromolecular Chain Transfer Agent (macroCTA) prepared by radical RAFT copolymerization, and (2) synthesis of a P(CTFE-alt-EVE) block by radical RAFT copolymerization from a PEVE macroCTA prepared by cationic RAFT polymerization. Careful chain-end analysis using 1H and 19F NMR spectroscopies revealed that irreversible transfer reactions severely affected the chain-end fidelity of the P(CTFE-alt-EVE) macroCTA. In addition, the penultimate CTFE unit of these macroCTAs seemed to adversely alter the reactivity of the –CH2-CH(OEt)-XA end-group under cationic RAFT conditions. The chain extension of these macroCTAs by cationic RAFT polymerization thus led to poorly defined block copolymers. Nevertheless, both xanthate and dithiocarbamate RAFT agents were shown to provide efficient control over the radical RAFT copolymerization of CTFE and EVE. In contrast, the cationic RAFT polymerization of EVE afforded PEVE macroCTAs with high chain-end fidelity and chain extension reactions resulting in well-defined PEVE-b-P(CTFE-alt-EVE) block copolymers with low dispersities (Đ < 1.35).

Self-assembly of poly(vinylidene fluoride)-block-poly(2-(dimethylamino)ethylmethacrylate) block copolymers prepared by CuAAC click coupling

Poly(vinylidene fluoride) (PVDF) is a very important fluoropolymer which possesses remarkable physico-chemical properties such as high thermal and chemical resistances as well as ferroelectricity, for example. To date, only iodine transfer polymerization and RAFT polymerization have enabled the preparation of well-defined PVDF and of some PVDF-based block copolymers (BCPs). However, these reversible deactivation radical polymerization techniques suffer from undesired reactions which impair the synthesis of a wide range of PVDF-containing BCPs. Here, unprecedented poly(vinylidene fluoride)-block-poly(2-(dimethylamino)ethylmethacrylate) (PVDF-b-PDMAEMA) BCPs were prepared by CuAAC click coupling of azide-functionalized PVDF synthesized by RAFT polymerization and alkyne-functionalized PDMAEMA synthesized by ATRP. This strategy was quite efficient and afforded three relatively well-defined BCPs (PVDF40-b-PDMAEMA23, PVDF40-b-PDMAEMA69, PVDF40-b-PDMAEMA162, Đ < 1.55). These amphiphilic BCPs were self-assembled in water at pH 2, 8 (native pH) and 10. The morphologies obtained were mainly polydisperse (20–500 nm), roughly spherical aggregates. However, at pH 8, PVDF40-b-PDMAEMA69 also formed micrometer-long rigid cylindrical micelles. These morphologies are likely the first examples of PVDF-containing BCP nanostructures produced by crystallization-driven self-assembly.

Photocrosslinked PVDF-based star polymer coatings: an all-in-one alternative to PVDF/PMMA blends for outdoor applications

A 4-arm star PVDF was synthesized as an appealing alternative to PVDF/PMMA blends since it provides crosslinked PVDF transparent coatings via photocrosslinking. The process is very fast and versatile, the resulting coating displays very good adhesion properties to a metal surface, and the surface energy and the water contact angle are easily tunable.

Well-defined poly(vinylidene fluoride) (PVDF) based-dendrimers synthesized by click chemistry: enhanced crystallinity of PVDF and increased hydrophobicity of PVDF films

This study reports the preparation by click chemistry of a novel fluorinated dendrimer bearing PVDF branches and its characterization by several analytical methods including 1H, 13C, 31P and 19F NMR, diffusional NMR, SEC, DLS, ATG, DSC and HRTEM. As remarkable properties, this dendritic PVDF displayed crystallinity (HRTEM highlighted crystalline disc-like zones of ca. 5 nm) and a much higher hydrophobicity than both its precursors with the water contact angle (WCA) reaching 108°.

Syntheses of 2-(trifluoromethyl)acrylate-containing block copolymers via RAFT polymerization using a universal chain transfer agent

This article describes the synthesis and characterization of a series of well-defined block copolymers (BCPs) comprising a poly(vinyl acetate-alt-tert-butyl-2-trifluoromethacrylate) (poly(VAc-alt-MAF-TBE)) alternating copolymer segment and a homopolymer segment (PVAc, polystyrene, poly(meth)acrylate, polyacrylamide, or poly(N-vinylpyrrolidone)) using RAFT polymerization under mild conditions (at 40 °C). The abilities of four chain transfer agents (CTAs) to copolymerize VAc and MAF-TBE were compared. Recently reported as a universal RAFT CTA, cyanomethyl 3,5-dimethyl-1H-pyrazole-1-carbodithioate (CDPCD) afforded better-defined BCPs compared to O-ethyl-S-(1-methoxycarbonyl)ethyldithiocarbonate (CTA-XA), 2-cyano-2-propyl benzodithioate (CPDB), and 4-cyano-4-(2-phenylethanesulfanylthiocarbonyl)sulfanyl pentanoic acid (PETTC). While the chain extension of poly(VAc-alt-MAF-TBE)-DPCD with vinyl acetate (VAc), styrene (St), n-butyl acrylate (nBA), and dimethyl acrylamide (DMA) led to well-defined poly(VAc-alt-MAF-TBE)-b-poly(M) BCPs with acceptable dispersity values (Đ ≤ 1.36), high Đ values were observed when methyl methacrylate (MMA) and N-vinylpyrrolidone (NVP) were used to form the second block. An attempt to synthesize poly(M)-b-poly(VAc-alt-MAF-TBE) block copolymers using poly(M)-DPCD as the macroCTA led to copolymers with high Đ values (1.53–2.0).