The use of ¹⁹F NMR for new structure determination in the radiolysis of FEP

The radiation chemistry of poly(tetrafluoroethylene-co-perfluoropropylene), FEP, with a mole fraction of tetrafluoroethylene, TFE, of 0.90 has been studied under vacuum using ⁶⁰Co γ-radiation over absorbed dose ranges up to 3.0 MGy. The radiolysis temperatures were 300, 363, 423 and 523 K. New structure formation in the copolymers was analyzed by solid-state ¹⁹F NMR. The new structures formed in the copolymers have been identified and the G-values for the formation of new -CF₃ groups was 2.2 at the lower temperatures and increased to 2.9 at 523 K. The G-value for the loss of original -CF₃ groups was ≈1.0 at all temperatures. At the lower temperatures there was a net loss of -CF- groups on irradiation; G(CF) of -1.3, -0.9 and -0.5 at 300, 363 and 423 K, respectively, but at 523 K there was a net gain with G(CF) equal to 0.8.