Study on Chemical Structures of Tetrafluoroethylene-Perfluoro-Alkyl-Vinylether Copolymer by EB-Irradiation in the Molten State

Perfluorinated polymers such as tetrafluoroethylene-perfluoroalkylvinylether copolymer (PFA) with remarkable chemical durability and thermal stability have been applied for industry. However, PFA has been classified to be typical radiation-degradable polymer. In our previous work, it has been found that crosslinked PFA has been obtained by irradiation under oxygen-free atmosphere in its molten state. In this study, the change of thermo-physical properties and the chemical structures of crosslinked PFA were studied by DSC and 19F-NMR. PFA was irradiated by soft electron beam (soft-EB) under nitrogen atmosphere at 583 K±3 K. By DSC analysis, the melting temperature (Tm) shifted to lower temperatures, and crystallinity decreased with increasing dose. Of course, in the case of room temperature irradiation, Tms were hardly changed, and crystallinity increased with increasing dose. For 19F-NMR spectroscopy, the several new signals, which should be due to the changed chemical structures, were observed besides the intense peak of CF2 at -124 ppm. The detected new signals assigned to the tertiary carbon (CF) group with Y-type crosslinking site and fluoro-propylene site, and chain end group, respectively. That is, it was found that the Y-type crosslinking reactions and chain scission should occur simultaneously in the melting temperature irradiation. The crosslinking density calculated by concentration of CF with Y-type crosslinking site increased with increasing of dose. The crosslinking density estimated for the 1200 kGy irradiated PFA showed about 1.03%