A NORMAL VIBRATIONAL ANALYSIS OF SYNDIOTACTIC POLYSTYRENE

A normal vibrational analysis has been performed for the all-trans conformation of syndiotactic polystyrene. In this analysis a set of nonredundant symmetry coordinates and force constants has been employed for the phenyl ring. The other force constants needed for the chain have been transferred from studies of alkanes and have been applied to many polymers such as polyethylene and polypropylene. Observed infrared and Raman data, including polarization characteristics, have been satisfactorily assigned. Several localized ring modes that are also present in atactic and isotactic polystyrene as well as in toluene have been identified. Other conformation-sensitive features, which are unique to the syndiotactic isomer, are identified. Polarized infrared data show that coextruded samples have nearly perfect orientation of the trans sequences with the plane of the rings normal to the chain axis. The orientation is seen to increase upon annealing at 200 °C due to an increase in crystallinity. Upon higher temperature annealing a melting point of 285 °C is observed. The theoretical modulus is calculated from the slope of the dispersion curve of the longitudinal acoustic vibration near the Brillouin zone center. A value of 67 GPa was obtained. © 1990, American Chemical Society. All rights reserved.