VIBRATIONAL ANALYSIS OF POLYTETRAFLUOROETHYLENE

With the aid of newly obtained Roman data, a normal coordinate analysis has been performed on the polytetrafluoroethylene (PTFE) molecule. Calculations were made for three different helix models including the 13/6,15/7, and planar zigzag. The frequencies corresponding to the 15/7 helix were fitted by adjusting the force field. The conformation was changed, and the changes in the frequencies for the 13/6 helix and the planar zigzag were calculated using the same force field. Changes predicted for the 13/6 helix from the normal coordinate calculations are not in agreement with those actually observed at the 19°C transition. It was therefore hypothesized that the changes in the infrared and Raman spectra at this transition were due to Raman thermal defects as suggested by Brown. The potential-energy distribution was obtained for the optically active modes of the 15/7 helix, and the eigenvectors were presented for the motions of the A modes. The dispersion curve for the 15/7 helix is presented, and the coupling which occurs between the chain stretch and the CF stretching modes is discussed.