Superior Thermostability and Hydrophobicity of Poly(vinylidene fluoride- co -fluoroalkyl 2-trifluoromethacrylate)

A 2-trifluoromethacrylate monomer containing a C 6 F 13 side chain, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl 2-(trifluoromethyl)acrylate (MAF-C 6 F 13 ) was synthesized and copolymerized with vinylidene fluoride (VDF). First, the preparation of MAF-C 6 F 13 was achieved by two different routes: (i) transesterification of tert- butyl 2-trifluoromethacrylate (MAF- t Bu) with C 6 F 13 C 2 H 4 OH (55% yield with ∼95% purity) and (ii) esterification of 2-trifluoromethacryloyl chloride with the same fluorinated alcohol, which gave higher yield (82%) and purity (99%). The radical copolymerization of MAF-C 6 F 13 with VDF was initiated by three different systems (two peroxypivalates and one highly branched fluorinated persistent radical, PPFR), a chain transfer agent (CF 3 I), at various polymerization temperatures (65–90 °C) and in three types of solvents. The relative comonomer incorporation and number-average molecular weights ( M n s) of the resulting random poly(VDF- co -MAF-C 6 F 13 ) copolymers were assessed by NMR spectroscopy. Both features alongwith polymerization yields were influenced by the polymerization temperatures and the nature of solvents. The M n values were further affected by the type of initiators and the use of chain transfer agent. When dimethyl carbonate was used as the solvent, lower (2–4 mol %) MAF-C 6 F 13 comonomer was incorporated compared to those reactions that involved 1,1,1,3,3-pentafluorobutane (5–33 mol %). Surprisingly, M n s of these copolymers increased with polymerization temperatures when the reactions were initiated by PPFR. Thus, the copolymerization carried out at 65 °C and initiated by PPFR led to a M n of 33 000 g mol –1, while those achieved at 90 °C yielded a M n of 61 700 g mol –1 . The thermostability of the obtained copolymers under air (the temperature for 10% weight loss, T d10% > 340 °C) was significantly improved compared to that of VDF copolymers containing 2-trifluoromethacrylic acid or MAF- t Bu. Surface hydrophobicity of these copolymers was superior than that of PVDF homopolymer. For example, poly(VDF- co -MAF-C 6 F 13 ) copolymer of 59,000 g mol –1 with 2 mol % MAF-C 6 F 13 only, displayed a higher static water contact angle (114°) than that of PVDF homopolymer (ca. 94°).