Synthesis and properties of poly(trifluoroethylene) via a persistent radical mediated polymerization of trifluoroethylene

Abstract

The conventional radical homopolymerization of TrFE initiated by a ˙CF₃ radical (generated in situ from perfluoro-3-ethyl-2,4-dimethyl-3-pentyl persistent radical, PPFR) is presented. Reactions were carried out at an increasing PPFR concentration (initial [TrFE]₀ : [PPFR]₀ molar ratios varying from 2.5 to 20.0 mol%) to influence the molar masses (M_n, ranging between 7700 and 38 100 g mol⁻¹). PTrFE homopolymer yields were high (76–87%). The microstructures of such synthesized PTrFEs were characterized by ¹H and ¹⁹F NMR spectroscopy. The generated PTrFE chains were exclusively terminated by CF₃ end-groups, as revealed by MALDI-TOF spectroscopy and NMR analysis, indicating that the ˙CF₃ radicals initiated the polymerization of TrFE. The addition of the ˙CF₃ radicals onto TrFE was predominantly regioselective (66%) leading mainly to a CF₃–CHF–CF₂–PTrFE homopolymer. Furthermore, the CF₃ end group could be used as an efficient label to determine the PTrFE molar masses by ¹⁹F NMR spectroscopy that also enabled us to assess the chain defects (14%). The thermal properties of these CF₃–PTrFE–CF₃ polymers revealed (i) a high thermal stability (their degradation under an oxidative atmosphere started from 362 °C and ranged even up to 428 °C for higher molar masses of PTrFEs) and (ii) a semi-crystalline behavior with a crystallinity rate averaging 36%.