Thermal effects on the strain-induced β to α form crystalline structural transition of solid-state syndiotactic polystyrene

Thermal effects on the strain-induced structural transition from β-form to α-form crystals of syndiotactic polystyrene (sPS) were investigated by changing the stretching temperature and the annealing temperature. When sPS was stretched at lower temperature (near the glass transition temperature (T_g) of sPS (∼130 °C)), the crystalline structural transition was incomplete, producing fragmented β-form and mesomorphic α-form crystals. Stretching at higher temperature facilitated the crystalline structural transition from β to α. For the sPS specimen stretched at 130 °C, the β-form crystals broke into small pieces, simultaneously creating mesomorphic α-form crystals. After annealing, the fragmented β-form crystals and the mesomorphic α-form crystals were reorganized to become complete crystals. The reorganization became more pronounced as the annealing temperature increased. The main role of the mechanical strain and the heat, therefore, could be the destruction of β-form crystals to produce fragmented β-form crystals and mesomorphic α-form crystals, and the formation of complete crystals, respectively.