Solvent induced crystallization and phase transition of syndiotactic polymethoxystyrene investigated using In situ wide angle X-ray diffraction

Abstract

Solvent induced crystallization and phase transition is an interesting phenomenon that has been observed in many kinds of semicrystalline polymer. In the case of syndiotactic polystyrene (SPS) which exhibits complicated phase transition behavior, this process may be different when the phenyl rings are substituted by polarity groups. In our previous work, the crystal structures of a series of –OCH₃ (OMe) substituted SPS and OMe-SPS/solvent complexes were analyzed (Macromolecules 2021, 54, 1881 and Macromolecules 2022, 55, 8222). In this particular work, the phase transition behavior of OMe-SPS, especially meta-OMe-SPS with different initial crystalline structures was discussed based on in situ 2-dimensional wide-angle X-ray diffractions (2D-WAXD) in the presence of organic solvent. It is found that meta-OMe-SPS in amorphous state and mesophase shows similar solvent induced phase transition like the cases of SPS. However Meanwhile, highly crystalline and oriented meta-OMe-SPS also exhibits organic solvent induced phase transition from β form with planar zigzag conformation into δ form with helical conformation, whichis has not been observed in SPS. The subsequent heating of meta-OMe-SPS δ and γ forms does not form β form, which is also unlike the situation of SPS δ/δ_e-γ-α/β transition. The OMe substituted group that changes the polarity of the phenyl rings may be the chemical structure region of affecting the chain conformation energy and phase transition behavior.