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.