An investigation of polytetrafluoroethylene (PTFE), nC20F 42, and a random copolymer of tetrafluoroethylene and hexafluoropropylene (TFE-HFP) under pressure has been carried out using Raman spectroscopy in conjunction with a diamond anvil cell. Both nC 20F42 and the TFE-HFP copolymer were found to undergo a phase transition in the 7-9 kbar range similar to PTFE as evidenced by the observation of the 625 cm-1 Raman band characteristic of phase III. With increasing pressure in the 10-52 kbar range, a continual variation in intensity of the bands at 285 and 395 cm-1 was observed and found to differ for the three fluorocarbon materials studied. By correlating a change in the I285/I395 ratio with a change in sample crystallinity (as determined by x ray), it has been determined that an increase in transplanar content with pressure is responsible for the observed band intensity changes in the high pressure phase of PTFE. © 1978 American Institute of Physic.