Abstract
Raman spectroscopic investigations of the high-pressure phase in polyethylene (PE) and each phase in poly(tetrafluoroethylene) (PTFE) under high pressure were performed using a hydrostatic high-pressure optical vessel. It was found that the molecular chain in the high-pressure phase of PE contains many gauche bonds similarly to the liquid phase, and it was confirmed that this phase is like a liquid crystal, which is consistent wih the other results of X-ray, optical microscopic, and ultrasonic experiments. In the case of PTFE, the behavior of the two weak bands at 581 and 601 cm−1, whose assignment has been the subject of discussion for some time in previous literatures, was investigated in detail throughout the whole range of PTFE phase diagram. It is suggested that the bands at 581 and 601 cm−1 should be attributed to 136 helical and transplanar conformations, respectively. Furthermore, the mechanism of untwisting in the PTFE molecular chain under high pressure is proposed.
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