γ線照射Polytetrafluoroethyleneの核磁気共鳴吸収 (II)

照射雰囲気効果

抄録

NMR absorption of polytetrafluoroethylene ⁶⁰Co γ-rays-irradiated with a total dose of about 2.2×10⁶R in the presence of oxygen or nitrogen gas, or in a high vacuum and then heat-treated .at 300°C in vacuum were measured. As to the effect of irradiation-atmosphere, a very remarkable increase in crystallinity and the step-like broadening of narrow line width above 27°C were observed in the specimens heat-treated after γ-irradiation in oxygen gas. In contrast there was no difference in molecular motion, between the specimen heat-treated after γ-irradiation in nitrogen gas and that in vacuum. This remarkable increase in crystallinity is ascribed to the scission of molecular chains -following the reaction of -CE₂-CF₂ radicals with oxygen. The step-like broadening of line width of narrow component is due to the superposition of narrow component and paracrystalline compo-nent which segregated from broad component in the vicinity of the room temperature transition. The most part of the increase in crystallinity was paracrystalline component produced as a result of the post-irradiation heat treatment. The segregation of paracrystalline component from broad component in the vicinity of the room temperature is due not only to chain alignment in order but also to the transition in molecular motion of the crystalline regions. The paracrystalline component is ascribed to the regions which consist of the shorter polymer chains orderly aligned and affected by the crystalline regions.