Crystallization and melting of α and β phases in bulk syndiotactic polystyrene as monitored in situ via high-temperature wide-angle X-ray diffraction

Direct and non-intrusive observations of crystallization and melting behavior of α and β polymorphs in bulk syndiotactic polystyrene were made by means of temperature-programmed x-ray diffraction. Results indicated that the highest sustainable temperature identifiable via wide-angle x-ray diffraction using stepwise annealing at increasingly higher temperatures (Ta) for the perfected (with the initial crystallization temperature Tc = 245 °C, followed by annealing at stepwise increased Ta above 250 °C) α″ phase may be at least 286 °C. In a similar manner, the highest sustainable temperature of the perfected (with Tc = 265 °C, followed by annealing at stepwise increased Ta above 275 °C) β′ phase may be at least 280 °C. These observations suggest complete melting should occur only above the respective sustainable temperatures. It thus follows that equilibrium melting of the α and the β phases should occur at temperatures higher than 286 and 280 °C, respectively. Perfection of the less ordered α′ form into the better ordered α″ form within the α family is observed to occur in the vicinity of 270 °C; no evidence of transformation between α and β phases is identified.