Nuclear Magnetic Resonance Absorption of Polytetrafluoro-ethylene γ-Irradiated at High Temperatures

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Abstract
The NMR spectra of PTFE irradiated at various temperatures with a dose of 1.1×107 R and irradiated at 340°C with various doses were measured over the temperature range from -50°C to 50°C. In the case of PTFE irradiated with 1.1×107 R, the percent crystallinity estimated from NMR spectra increased with increasing irradiation temperature up to about 300°C, but decreased abruptly above 320°C, and increased again. In the case of PTFE irradiated at 340°C, the crystalline transition temperature was shifted to a lower temperature at 1.1×107 R and the NMR line shape changed into a single component at 1.1×108 R. The crystal imperfections due to irradiation at 340°C were caused by high viscosity during irradiation, occlusion of low molecular degradation products, the low degree of chain fractures and probably by the structure changes such as branches, crosslinkings, etc.