Crystalline Transitions of the Clathrate (δ) Form of Syndiotactic Polystyrene during Heating:  Studies Using High-Temperature X-ray Diffraction

Abstract

The structural changes occurring during heating in a syndiotactic polystyrene (sPS)−solvent complex were monitored in situ by X-ray diffraction. The room temperature δ form transformed into the γ form on heating above the glass transition temperature of the sPS. The transition temperature showed a linear dependency on the amount of solvent absorbed; the higher the solvent molecules absorbed, the higher the transition temperature. However, the transition temperature does not depend on the nature of the solvent. The emptied clathrate form transformed into the γ form at the glass transition temperature. The γ form transformed into the α‘ ‘ form at ∼200 °C on heating and is independent of the δ to γ form transition. Calorimetric studies showed an endotherm followed by an exotherm during these transitions and indicated that the transitions are first order in nature.The studies provided information on the stability of various crystalline forms of sPS.