Bruno Ameduri

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.

Towards new strategies for the synthesis of functional vinylidene fluoride-based copolymers with tunable wettability

Synthesis of poly(vinylidene fluoride)-based functional polymers with tunable wettability was achieved via radical copolymerizations of vinylidene fluoride (VDF) with tert-butyl 2-trifluoromethacrylate (MAF-TBE) followed by hydrolysis of the tert-butyl ester groups. Radical copolymerizations of VDF with 2-trifluoromethyl acrylic acid (MAF) and MAF-TBE were investigated under various experimental conditions: initiators, temperatures, and solvents. The polymerizations using peroxide initiators led to good yield (≥57%), while azo initiators did not lead to any polymerization. The compositions and microstructures of all the obtained copolymers were determined by 1H and 19F NMR spectroscopies. The very low yield (23%) achieved in radical copolymerization of VDF with MAF in water was attributed to the regioselective nucleophilic addition of water onto MAF, yielding a potential fluorosurfactant, 3-hydroxy-2-(trifluoromethyl)propanoic acid in good yield (85%). In contrast, no reaction was observed between MAF-TBE and water, even in the presence of ammonium perfluorooctanoate as a (fluorinated) surfactant. The poly(VDF-co-MAF-TBE) copolymer was shown to be easily hydrolyzed under mild conditions to prepare –COOH-functionalized PVDF copolymers, without any dehydrofluorination of VDF units. The wettabilities of these copolymers were studied by water contact angle (WCA) measurement. Compared to the poly(VDF-co-MAFTBE) copolymers (WCA = 102°), the –COOH functionalized PVDF copolymer exhibits a lower WCA (57°). This work paves the way for the synthesis of PVDF-based functional copolymers with tunable wettability for potential applications in the preparation of membranes for water purification, coatings or oil recovery systems.

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.

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.

Kinetic and mechanistic aspects of the iodine transfer copolymerization of vinylidene fluoride with 2,3,3,3-tetrafluoro-1-propene and functionalization into ω-hydroxy fluorinated copolymers

The synthesis of functional poly(VDF-co-1234yf) copolymers bearing –OH end groups was achieved via iodine transfer copolymerizations of vinylidene fluoride (VDF) with 2,3,3,3-tetrafluoro-1-propene (1234yf) followed by selective post-functionalization. First, free radical copolymerization (FRP) (in the absence of a chain transfer agent (CTA)) of VDF with 1234yf was investigated under different experimental conditions: varying the comonomer feed ([VDF]0/[1234yf]0) ratio led to several poly(VDF-co-1234yf) copolymers with molecular weights (Mn) ranging between 4600 and 12u2006400 g mol−1, dispersities (Đ) of ca. 2.05, and fair to good conversions (45–77%). Thermoplastic crystalline powders were obtained when the mol% of VDF in the copolymers was higher than 85%, while amorphous copolymers contained a lower mol% of VDF. This study also reports for the first time the determination of reactivity ratios (rVDF = 0.76 ± 0.34 and r1234yf = 1.23 ± 0.17 at 74 °C). Subsequently, iodine transfer polymerization (ITP) of VDF and 1234yf in the presence of 1-iodoperfluorohexane as the CTA in 1,1,1,3,3-pentafluorobutane and even in water using potassium persulfate as the initiator without any surfactant led to satisfactory yields (ca. 80%), Mn up to 4100 g mol−1 and a narrow Đ (ca. 1.35). A detailed kinetic study of ITP enabled assessing the chain transfer constant of C6F13I, CTr = 7.4, at 74 °C. The compositions and microstructures of all the obtained copolymers were determined by 1H and 19F NMR spectroscopies. Finally, chemical modification of the iodide end functionality of the poly(VDF-co-1234yf)–I copolymer into a primary hydroxyl end group was achieved by radical addition of these iodinated poly(VDF-co-1234yf) copolymers onto allyl alcohol, followed by selective reduction of iodine atoms.

Comparison of Surface and Bulk Properties of Pendant and Hybrid Fluorosilicones

The most common fluorosilicone polymer commercialized to date is polymethyltrifluoropropylsiloxane. However, the low content of is the perfluorinated groups in the polymer 36.5 wt% does not fulfill the requirements of some high tech applications, particularly when swelling properties or degradation at high temperatures are concerned. A number of strategies have been employed to increase the fluorine content of fluorosilicone polymers. One elegant way is to introduce into the silicone chain, either as a pendant group or inside the backbone, perfluorinated groups of increasing size (typically C6 or higher). We refer to silicones with perfluorinated chains introduced as side groups as “pendant silicones” whereas those carrying fluorine atoms in the main backbone are called “hybrid silicones”. The most popular synthesis techniques of such polymers are briefly discussed here. A full fuller comparison is given of the two classes of polymers in terms of surface, mechanical, swelling and thermal properties.

Organometallic‐Mediated Radical Polymerization of Vinylidene Fluoride

An unprecedented level of control for the radical polymerization of vinylidene fluoride (VDF), yielding well-defined PVDF (at least up to 14u2009500u2005gu2009mol-1 ) with low dispersity (≤1.32), was achieved using organometallic-mediated radical polymerization (OMRP) with an organocobalt compound as initiator. The high chain-end fidelity was demonstrated by the synthesis of PVDF- and PVAc-containing di-and triblock copolymers. DFT calculations rationalize the efficient reactivation of both head and tail chain end dormant species.

Styrene and substituted styrene grafted functional polyolefins via nitroxide mediated polymerization

The grafting of (functionalized) polystyrene from bulk or surface-functionalized polyolefins via nitroxide mediated polymerization is described. High density polyethylene and a poly(ethylene-co-α-olefin) copolymer (EOC) modified with different functional 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO) derivatives were used as macroinitiators for the “grafting from” polymerization of various styrene-based monomers to yield polyolefin-g-polystyrene graft copolymers. The successful grafting of styrene and styrene derivatives was demonstrated by complementary analyses such as infrared (ATR-FTIR) and NMR spectroscopy, size exclusion chromatography, thermogravimetric analysis, and differential scanning calorimetry. Typically, IR spectroscopy of the grafted copolymers showed the bands attributable to the aromatic moieties and the obtained thermograms evidenced a lower degradation temperature for the grafted copolymers compared to that of polyolefin starting materials. In addition, solid state 19F-NMR was chosen to confirm the growth of polystyrene (PS) chains when EOC functionalized with a fluoroalkyl TEMPO was used for NMP. The extent of grafting of PS chains onto the polyolefin backbone was found to depend on the nature of the macroinitiator, especially on the structure and cleavage temperature of alkoxyamine derivatives created by TEMPO functionalization, on its content and on the adopted experimental conditions.

Poly(fluoroacrylate)s with tunable surface hydrophobicity via radical copolymerization of 2,2,2-trifluoroethyl α-fluoroacrylate and 2-(trifluoromethyl)acrylic acid

The synthesis of poly(fluoroacrylate)s with tunable wettability and improved adhesion for potential application as functional coatings was achieved via radical copolymerization of 2,2,2-trifluoroethyl α-fluoroacrylate (FATRIFE) with 2-(trifluoromethyl)acrylic acid (MAF), an adhesion-promoting monomer. These copolymerizations, initiated by tert-butyl peroxypivalate at varying comonomer feed ([FATRIFE]0/[MAF]0) ratios led to a series of poly(FATRIFE-co-MAF) copolymers with different molar compositions in fair to good conversions (32–87%) depending on the MAF feed content. The microstructures of the synthesized poly(FATRIFE-co-MAF) copolymers were determined by 19F NMR spectroscopy. Even at MAF feed contents higher than 50%, MAF incorporation into the copolymers was lower than 50%, since MAF does not undergo any homopolymerization under radical polymerization conditions. The reactivity ratios of the (FATRIFE; MAF) monomer pair were also determined (rFATRIFE = 1.65 ± 0.07 and rMAF = 0 at 56 °C) evidencing the formation of statistical copolymers. Initiation involving a highly branched perfluorinated radical that released a ˙CF3 radical enabled the demonstration of the regioselective attack of the latter radical onto the CH2 of FATRIFE. The resulting poly(FATRIFE-co-MAF) copolymers exhibited various glass transition temperatures (Tgs) depending on their compositions. Tg values increased with increasing MAF contents in the copolymer. In addition, their thermal stability (the temperature for 10% weight loss in air, Td10%) increased with increasing FATRIFE content in the copolymer and reached 348 °C (for that containing 93 mol% FATRIFE). Finally, a high copolymer MAF content led to both a good adhesion onto metal substrates and to improved hydrophilicity, as revealed by the decrease of the water contact angle from 107° (for a reference PFATRIFE homopolymer) to 81° (for a copolymer containing 42 mol% MAF).