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

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journal contribution
posted on 14.01.2014, 00:00 authored by Mohan N. Wadekar, Yogesh R. Patil, Bruno Ameduri
A 2-trifluoromethacrylate monomer containing a C6F13 side chain, 3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyl 2-(trifluoromethyl)­acrylate (MAF-C6F13) was synthesized and copolymerized with vinylidene fluoride (VDF). First, the preparation of MAF-C6F13 was achieved by two different routes: (i) transesterification of tert-butyl 2-trifluoromethacrylate (MAF-tBu) with C6F13C2H4OH (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-C6F13 with VDF was initiated by three different systems (two peroxypivalates and one highly branched fluorinated persistent radical, PPFR), a chain transfer agent (CF3I), at various polymerization temperatures (65–90 °C) and in three types of solvents. The relative comonomer incorporation and number-average molecular weights (Mns) of the resulting random poly­(VDF-co-MAF-C6F13) copolymers were assessed by NMR spectroscopy. Both features alongwith polymerization yields were influenced by the polymerization temperatures and the nature of solvents. The Mn 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-C6F13 comonomer was incorporated compared to those reactions that involved 1,1,1,3,3-pentafluorobutane (5–33 mol %). Surprisingly, Mns 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 Mn of 33 000 g mol–1, while those achieved at 90 °C yielded a Mn of 61 700 g mol–1. The thermostability of the obtained copolymers under air (the temperature for 10% weight loss, Td10% > 340 °C) was significantly improved compared to that of VDF copolymers containing 2-trifluoromethacrylic acid or MAF-tBu. Surface hydrophobicity of these copolymers was superior than that of PVDF homopolymer. For example, poly­(VDF-co-MAF-C6F13) copolymer of 59,000 g mol–1 with 2 mol % MAF-C6F13 only, displayed a higher static water contact angle (114°) than that of PVDF homopolymer (ca. 94°).