Crystal Structure of High Pressure Phase of Polytetrafluoroethylene

Abstract

The crystal structure of high pressure phase of polytetrafluoroethylene (PTFE) has been determined by X-ray methods. A high pressure X-ray diffraction apparatus which enables to get the fiber pattern of crystalline sample under purely hydrostatic high pressure at high temperature has been constructed. A small specimen of PTFE fiber was held in the bore of a beryllium window for X-ray. The fiber pattern of high pressure phase of this polymer has been recorded on a cylindrical film at 5500km/cm2, 78°C. It is found that in this phase the molecules have a planar zigzag arrangement different from that of a helix at atmospheric pressure. The unit cell is orthorhombic, with a=8.73 A, b=5.69 A, c=2.62 A. The result of the X-ray diffraction studies agrees with that of the other physical properties of PTFE in high pressure phase.