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

Abstract

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.