Crystalline morphology and melting behavior of 100% syndiotactic polystyrene and 70/30 blend of syndiotactic polystyrene and poly(2,6-dimethyl-1,4-phenylenoxide)

Abstract

The thermal behavior of isothermally crystallized syndiotactic polystyrene (SPS) and 70/30 SPS/poly (2,6-dimethy 1-1,4-diphenylene oxide) (PPO) blend was investigated by differential scanning calorimetry. Pure SPS, which was crystallized at T-c = 220 and 240 degrees C had single melting endotherm and multiple endotherms, respectively, whereas the 70/30 SPS/PPO blends showed the opposite behavior with respect to T-c. Investigation by polarizing optical microscopy and small angle X-ray scattering revealed that the rejected impurity (PPO in blend and noncrystallizable chains with low molecular weight in pure SPS) during SPS crystallization resides between primary lamellae of SPS and thus the recrystallization strongly suppressed for the pure SPS crystallized at T-c = 220 degrees C and the 70/30 SPS/PPO blend crystallized at T-c = 240 degrees C. This may induce single melting endotherm. In the pure SPS crystallized at T-c = 240 degrees C and the 70/30 SPS/PPO blend crystallized at T-c = 220 degrees C, the rejected impurity resided between SPS crystalline fibrils, which consist of lamellae. This may allow recrystallization between the primary lamellae which would exhibit sharp multiple melting endotherms.