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 alpha and beta 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 (T-a) for the perfected (with the initial crystallization temperature T-c=245 degreesC, followed by annealing at stepwise increased T-a above 250 degreesC) alpha" phase may be at least 286 degreesC. In a similar manner, the highest sustainable temperature of the perfected (with T-c= 265 degreesC, followed by annealing at stepwise increased T-a above 275 degreesC) beta' phase may be at least 280degreesC. These observations suggest complete melting should occur only above the respective sustainable temperatures. It thus follows that equilibrium melting of the alpha and the beta phases should occur at temperatures higher than 286 and 280degreesC, respectively. Perfection of the less ordered alpha' form into the better ordered alpha" form within the alpha family is observed to occur in the vicinity of 270 degreesC; no evidence of transformation between alpha and beta phases is identified.