Molecular motion in polytetrafluoroethylene at cryogenic temperatures

Speculation is offered on the nature of the molecular motion in crystals of polytetrafluoroethylene at temperatures well below the 19°C transition. It is proposed that a specific type of defect in the chain, a helix reversal point, creates a mechanism whereby large dynamic angular displacements of chain segments about their long axes can occur without significantly affecting the X-ray diffraction data.