Synthesis of ω-Iodo and telechelic diiodo vinylidene fluoride-based (co)polymers by iodine transfer polymerization initiated by an innovative persistent radical

Abstract

The synthesis of ω-iodo and telechelic diiodo vinylidene fluoride (VDF)-based (co)polymers by iodine transfer polymerization (ITP) of VDF initiated by a trifluoromethyl radical (generated by perfluoro-3-ethyl-2,4-dimethyl-3- pentyl persistent radical, PPFR) is presented. Reactions were carried out in the presence of different chain transfer agents (CTAs, such as trifluoroiodomethane, 1,4-diiodoperfluorobutane, and molecular iodine) with/without tert-butyl 2-trifluoromethacrylate (MAF-TBE). Experimental conditions (nature of the solvents and CTAs, time, temperature, and initial [VDF]0:[CTA]0:[initiator]0 molar ratios) were varied to influence the yield of the reaction (up to 86%), the molar masses (Mn), dispersity values (), chain end functionalities, and microstructures of the obtained polymers. Detailed kinetics study enabled to confirm the well-controlled polymerization: (i) synthesis of iodinated polymers with different molar masses (Mn,SEC = 1110-5800 g mol-1) and low values (≤1.30), just simply by varying the [VDF]0:[CTA]0 initial molar ratio; (ii) linear increase of Mn versus conversion, maintaining low values (≤1.28); (ii) the presence of favored -CH2CF2-I end functionality up to 80% monomer conversion. The compositions and microstructures of all the obtained copolymers were characterized by 1H and 19F NMR spectroscopies. Deeper mechanistic investigation of the ITP of VDF initiated by •CF3 radical from PPFR was carried out. In the presence of CF3I as the CTA, the competitive presence of CF3 end group in CF3-PVDF-I was evidenced to arise from the CTA and showed a negligible amount of CF3-PVDF oligomer dead chains initiated from •CF3 radical from PPFR. Very low chain defects (due to reversed -CH2CF2- CF2CH2- And -CF2CH2-CH2CF2- in VDF-VDF dyads, even the absence of such a later one) led to high melting points (161-173 °C) of the resulting polymers, as revealed by differential scanning calorimetry. The thermal stability of the polymers increased with higher Mn values reaching 270 °C under air, while for copolymers containing MAF-TBE, the degradation occurred from 170 °C attributed to the release of isobutene from the tert-butyl side groups.