Study on the synthesis of perfluorovinyl‐sulfonic functional monomer and its copolymerization with tetrafluoroethylene

Tetrafiuoroethylene (TFE) and hexafluoropropylene (HFP) were subjected to reactions with freshly distilled sulfur trioxide to obtain 1‐fluorosulfonyldifluoro‐acetylfluoride (FSDFAF, yield 65–70%) and pentafluoro‐2‐propenylfluorosulfate (PPFS, yield up to 50%). A subsequent reaction of FSDFAF with PPFS under anhydrous conditions led to a preparation of 2‐(1‐pentafluoro‐2‐propenyloxy)tetrafluoroethanesulfonyl fluoride (PPOTESF, yield 40–41%) whose structure was proved by both infrared (IR) spectroscopy and nuclear magnetic resonance ( 19 F NMR). TFE was copolymerized with PPOTESF in bulk by using a free radical initiator of the hydrocarbon type at a temperature of 50°C. Various TFE/PPOTESF mole ratios were employed and the presence of sulfonyl fluoride (SO 2 F) functional groups in the copolymers was proven by IR spectroscopy. The copolymers were subjected to alkaline hydrolysis and the SO 2 F content was found not to exceed 0.70–0.80 mEq/g with polymer yields in the range of 11–31%. The reactivity ratios r 1 and r 2 related to TFE and PPOTESF, respectively, were determined by using the Fineman‐Ross method. A random distribution of PPOTESF units along the polymeric chain, consisting mainly of TFE fragments, was found to exist. The copolymers had melting temperatures 40–45°C lower than polytetrafluoroethylene and were thermally stable to 305–315°C.