β to α Form Transition Observed in the Crystalline Structures of Syndiotactic Polystyrene (sPS)

A solid−solid crystalline transition from β to α forms in syndiotactic polystyrene (sPS) was found during the mechanical deformation in the temperature range of 130−218 °C, studied by X-ray and infrared spectroscopy. α and β forms, in contrast to the other two crystalline structures (γ and δ forms) in sPS, are two major crystalline forms manufactured through a concise molding process which is industrially readily accessible. There have been a number of structural transitions found between two crystalline structures among the four different crystalline forms of sPS. In this work, β to α form transition at well below the melting temperature of sPS (∼270 °C) was found by mechanical deformation, which became more pronounced as temperature increased. The structural transition was intimately related to the crystallization temperature and the densities of α and β forms.