CONFORMATIONAL ORDERING PROCESS ON PHYSICAL GELATION OF SYNDIOTACTIC POLYSTYRENE SOLVENT SYSTEMS REVEALED BY TIME-RESOLVED INFRARED-SPECTROSCOPY

Syndiotactic polystyrene (SPS) dissolved in various organic solvents forms stable gels. Infrared spectroscopic research shows that SPS molecules assume highly ordered TTGG conformation in gels, giving rise to many infrared bands characteristic of the regular TTGG sequences. The behavior of the conformational ordering is strongly dependent on the solvent and the temperature. The time evolution of the conformational order on gelation has been investigated for SPS/CHCl3 systems at various polymer concentrations and temperatures by time-resolved infrared spectroscopy. By the analysis of the rate of formation of the ordered conformation derived from the time-resolved intensity measurement of the conformation-sensitive band at 572 cm-1, the number of the chain segments that contribute to the formation of clusters having ordered TTGG conformation has been evaluated as a function of temperature. The results indicate that at a temperature around 10-degrees-C the conformation ordering proceeds through clustering of five chain segments. The number decreases with lowering temperature and becomes unity below a certain temperature, suggesting that the ordering proceeds via self-organization within one chain. Such a crossover between the two mechanisms is found for other solvents, although the crossover temperature depends on the solvent. It has been concluded that strong interactions between polymer and solvent molecules play important roles in controlling the gelation behavior of SPS/solvent systems.