Microwave-Assisted oxidative degradation of poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene): Preparation, characterization, and reaction mechanism

Abstract

In this study, microwave (MW)-assisted oxidative degradation of poly(vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene) (P(VDF-TFE-HFP)) was applied to synthesize carboxy-terminated liquid fluororubber, referred to as LTCFs-246. The resulting product has a carboxyl content of 3.01%, a number-average molecular weight (Mn) of 2100 g/mol, and a polydispersity index (PDI) of 1.61. The product's structure was characterized and analyzed in detail using techniques such as ¹⁹F NMR, UV–Vis, and FTIR spectroscopy. Results indicate that the selective dehydrofluorination reaction (K_HF reaction) primarily occurs on four sequence structures: HFP-VDF-HFP, HFP-VDF-TFE, TFE-VDF-HFP, and TFE-VDF-TFE, with similar degrees of reactivity across these structures. Two types of C=C bonds were formed in the LTCFs-246 backbone, primarily through Hofmann elimination and, to a lesser extent, Zaitsev elimination. The oxidative reaction (K_C-C reaction) was temperature-dependent. At lower temperatures, H₂O₂ decomposed slowly, limiting the K_C-C reaction; as the temperature increased, H₂O₂ rapidly decomposed, actively engaging in the K_C-C reaction and extensively consuming C=C bonds. Once H₂O₂ was fully consumed, the K_C-C reaction ceased, while the K_HF reaction continued uninterrupted. In conclusion, this study provides strong evidence to advance the understanding of the oxidative degradation mechanism of MW-assisted P(VDF-TFE-HFP).