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 delta phase crystallized from toluene solution. The Bragg distance of 010 and (2) over bar 10 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 delta 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 delta phase crystal to the alpha or gamma 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 delta phase to the gamma phase at more than 150 degrees C. Crystallinity of St/BuSt in the gamma phase was lower than that in the delta phase. (c) 2018 Society of Chemical Industry