AbstractThe radiation chemistry of poly(tetrafluoroethylene‐co‐hexafluoropropylene) (FEP) with a TFE mole fraction of 0.90 has been studied under vacuum using 60Co γ‐radiation over a range of temperatures and absorbed doses. The radiolysis temperatures were 300, 363, 423, 523 and 543 K. New structure formation in the copolymers was analysed by solid‐state 19F NMR spectroscopy. The new structures formed in the copolymers have been identified and the G‐values for the formation of new chemical structures have been investigated at 363 and 523 K. These two temperatures are just above and just below the polymer Tg and Tm, respectively. At the lower temperature, there was no evidence for any chain branching and an estimate of G(S) of 1.0 was obtained. A value of G(S) of 1.3 and a minimum value of G(X)Y of 1.3 were obtained at 523 K. Copyright © 2003 Society of Chemical Industry