Vibrational Spectra of Polytetrafluoroethylene: Effects of Temperature and Pressure

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Abstract
The infrared spectrum of polytetrafluoroethylene was investigated as a function of temperature at low pressure, and as a function of pressure at ambient temperature. The temperature dependence of absorption in the region 625–640 cm—1 is consistent with the suggestion that the band at 625 cm—1 is due to a defect with creation energy ε≈0.05 eV. A calculation of the energy increase accompanying reversal of the pitch of the molecular helix supports this suggestion. At T≈100°K, there are resolved a number of bands in the region 700–1700 cm—1 that are not apparent at ambient temperature. For T>600°K, the spectrum was found to be significantly different from a report in the literature. Application of pressure p>6 kbar results in significantly reduced absorption at 640 and 1210 cm—1. The changes with pressure support the suggestion of a planar conformation of the molecule in a phase existing only at high pressure. The Raman spectrum exhibited lines at 733 and 1378 cm—1, in good agreement with predictions based upon combination bands in the infrared spectrum.

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