Thermal Transitions of ε Crystalline Phases of Syndiotactic Polystyrene

Thermal transitions of the three crystalline phases (γ, δ, and ε) of syndiotactic polystyrene (s-PS), presenting s(2/1)2 helices, have been compared by X-ray diffraction, differential scanning calorimetry (DSC), and dynamic-mechanical analyses. These analyses have been conducted on crystalline (δ and ε) films, obtained by similar solvent sorption and desorption procedures, starting from a same γ-form film. The Fourier transform Infrared (FTIR) spectra of the three films have also been compared. The obtained results indicate that the recently discovered ε-phase, as the already known δ-phase, is transformed in γ-phase by heating above 100 °C. However, the ε → γ transition occurs directly without the formation, for intermediate temperatures, of a helical mesomorphic phase, as instead observed for the δ → γ transition. DSC studies and FTIR measurements also suggest that the crystalline packing of the ε-form could be rather similar to that one of the γ-form.