Yi Wei, Yucai Ke, Xinyu Cao, Yongmei Ma, Fosong Wang, Effect of benzoylation on crystallinity and phase transition behavior of nanoporous crystalline form of syndiotactic polystyrene. Polymer 2013, 54, 958-963.

Abstract

In order to improve the thermal stability of δ_e form of sPS that possesses nanoporous structure, benzoylation of the phenyl groups was adopted and performed by solution procedure or solid procedure. The solution procedure involves initial benzoylation of sPS in solution and then preparing δ_e form by solvent induction of benzoylated sPS; the solid procedure means benzoylation of δ_e form of sPS in solid state. Usual modifications of sPS by solution procedure greatly decrease the crystallinity of the nanoporous related δ_e form. In this work, sPS can well maintain its crystallinity of δ_e form after benzoylation by solution procedure, even when benzoylation degree reaches 20%. Thermally induced phase transition behaviors of corresponding δ_e form were investigated by Differential scanning calorimeter and temperature-dependent X-ray diffraction analysis. The results show that the δ_e–γ transition temperature increases after benzoylation by both two procedures, indicating improved thermal stability of δ_e form. The subsequent γ–α transition and the melting of α form both shift to lower transition temperature. Meanwhile, the transition of δ_e form to γ form was prohibited by solution procedure contrast to solid procedure.