Radical Terpolymerization of 1,1,2-Trifluoro-2-pentafluorosulfanylethylene and Pentafluorosulfanylethylene in the Presence of Vinylidene Fluoride and Hexafluoropropylene by Iodine Transfer Polymerization

Abstract

Iodine transfer terpolymerization of two monomers bearing an SF5 group, i.e., 1,1,2-trifluoro-2-pentafluorosulfanylethylene (F2CCFSF5) and pentafluorosulfanylethylene (H2CCHSF5), with 1,1-difluoroethylene (or vinylidene fluoride, VDF) and hexafluoropropylene (HFP) is presented. These pentafluorosulfanyl monomers present a peculiar reactivity. They do not homopolymerize by conventional radical polymerization, but they co- and terpolymerize with the above fluorinated olefins. The resulting fluorinated terpolymers were characterized by 19F and 1H NMR spectroscopies which enabled the assessment of the molar percentages of the three comonomers. Size exclusion chromatography and NMR characterizations were also used to assess the molecular weights, Mn, ranging between 260 and 8400 g/mol. Interestingly, both these pentafluorosulfanyl monomers exhibit different behaviors in that radical terpolymerization in the presence of C6F13I as a degenerative chain transfer agent. Thus, CF2CFSF5 can be terpolymerized with VDF and HFP with a good control of molecular weight leading fluoropolymers bearing SF5 groups with low polydispersity index (PDI). Unexpectedly, only two iodide functionalities of the terpolymers namely two end groups (−CH2CF2I and −CF2CH2I) were observed and their proportions were influenced by the number of VDF units. Indeed, −CH2CF2I functionality decreased when the number of VDFs per chain increased. In contrast to 1,1,2-trifluoro-2-pentafluorosulfanyl ethylene, H2CCHSF5 could not be terpolymerized by ITP but led to C6F13[(CH2CF2)(CH2CH(SF5)]nI alternating cooligomers of low molecular weight in poor yields (5−20%). The formation of byproduct (C6F13CHCHSF5 monoadduct obtained by dehydrofluorination) was also observed, which corresponds to the elimination of HI from the 1:1 adduct. In the last part, the thermal properties are discussed. The presence of SF5 group decreases the Tg of fluoropolymers whereas the thermal stabilities depended on the molecular weights.