Crystalline structure and phase transition of syndiotactic styrene-based copolymers

Crystalline structure and phase transition of clathrate phase of syndiotactic poly[styrene-co-(p-R-styrene)] (St/RSt; R = CH₃ (Me), tert-butyl (Bu), HO), prepared from solutions, have been investigated with wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry. The copolymers containing less than 67.2 mol% of MeSt or 9.4 mol% of BuSt formed δ phase crystallized from toluene solution. The Bragg distance of 010 and (Formula presented.) reflections of the St/MeSt copolymer slightly increased with increasing of the MeSt content over 10 mol%. The St/HOSt copolymer containing 16.1 mol% of HOSt crystallized from dioxane solution also formed δ phase crystal. The orientation of the crystalline phase of the copolymers in films, which were prepared by cast-crystallization from o-xylene or dioxane solution, was evaluated using WAXD. The degrees of orientation were almost independent of RSt content in the copolymers. Phase transition from the δ phase crystal to the α or γ phase crystal of the copolymers in the heating process was observed using WAXD. The copolymers containing less than 14.8 mol% of MeSt or 8.4 mol% of BuSt showed a transition from the δ phase to the γ phase at more than 150 °C. Crystallinity of St/BuSt in the γ phase was lower than that in the δ phase.