Effect of benzoylation on crystallinity and phase transition behavior of nanoporous crystalline form of syndiotactic polystyrene

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