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Effect of γ-Irradiation on the Crystalline Transition Temperature in Poly(tetrafluoroethylene)

The effect of γ-irradiation on the 19°C transition of poly(tetrafluoroethylene) was studied with broad-line NMR and the transition temperature was measured as a function of total dose up to 109R. The transition temperature is lowered with increasing dose in all the following cases: (a) room-temperature irradiation, (b) room-temperature irradiation with subsequent annealing, and (c) irradiation above the melting point. In case (b), the lowering of the transition temperature is attributed to the mainchain scission in the crystalline phase. In case (a), in addition to the scission, the occlusion of degradation products is effective, and in case (c), the formation of side-branches (—CF3) plays an important role. The results are analysed by a theory of rotational phase transition and a satisfactory agreement between theory and experiment is obtained.