Molecular conformation in glasses and gels of syndiotactic and isotactic polystyrenes

Local and long-range conformational structures of syndiotactic (SPS), isotactic (IPS), and atactic polystyrene (APS) molecules in the glassy state were investigated by means of infrared and low-frequency Raman spectroscopy. The content of trans skeletal C--C bonds, estimated from the infrared absorption intensities, was found to be richer in SPS glass than in IPS glass. The infrared spectrum of an APS sample was reproducible by the superposition of the spectra of IPS and SPS glasses in the ratio of its diad tacticity measured by exp 13 C NMR. The stiffness of disordered chain segments estimated from the "disordered longitudinal acoustic mode" (D-LAM) frequency, and the specific volume of glassy samples, was found to increase in the order of IPS < APS < SPS. It was shown that by allowing SPS solutions to stand at room temperature a clear gel was formed, as in the case of decalin solution of IPS. Infrared spectra of SPS gels formed from different solvents were essentially identical with one another and were very close to that of the crystalline beta modification containing predominantly TTGG conformations, suggesting the presence of gel-forming coagulates containing highly ordered TTGG conformations. Differences in the behavior and structure between the SPS and IPS gels are considered in relation to the molecular mechanism of the gelation process. . 26 ref.--AA