Free-radical evolution and decay in cross-linked polytetrafluoroethylene irradiated by gamma-rays

Electron spin resonance techniques were employed to investigate the effects of the absorbed dose and post-irradiation conditions on the evolution and decay of free-radicals in cross-linked polytetrafluoroethylene (XPTFE), induced by gamma-ray radiation. Chain-end free-radicals, chain alkyl free-radicals, and tertiary alkyl free-radicals were detected when XPTFE was irradiated under Ar atmosphere. The corresponding peroxy free-radicals were formed upon exposure of irradiated XPTFE to air; the freeradicals concentration first increased linearly with increasing absorbed dose and then gradually saturated. The free-radicals yield under air atmosphere was greater than that under Ar, and the peroxy free-radicals were preserved for a relatively long time when irradiated XPTFE was stored under air atmosphere. The chain alkyl free-radicals may be converted to chain end free-radicals by beta-scission, while chain end free-radicals are more sensitive to oxygen than chain alkyl free-radicals. When the annealing temperature was raised above the alpha-transition temperature of XPTFE, the decay of the free-radicals was greatly affected and accelerated by the motion of the molecules over the long range.