An in situ SAXS/WAXS/Raman spectroscopy study on the phase behavior of syndiotactic polystyrene (sPS)/solvent systems: Compound formation and solvent (dis)ordering

In situ small- and wide-angle X-ray scattering (SAXS and WAXS) experiments combined with Raman spectroscopy and thermal analysis have been performed to study the phase behavior of syndiotactic polystyrene (sPS) solutions. Three different solvents were used respectively, decalin, benzyl methacrylate, and cyclohexyl methacrylate. When sPS solutions are quenched gel formation occurs. In these gels sPS adopts a helical conformation that is stabilized by the solvent molecules; in fact, compound formation occurs. From the combined experimental data it was concluded that two different structural modifications exist within the solvent-included helical δ-phase, respectively the δ′-phase, in which the solvent molecules are intercalated and ordered between the phenyl rings of sPS, and a δ″-phase, where the solvent ordering is lost. The so-called γ-phase, the solvent-free helical phase, was not observed in our studies. Transformation from the helical (δ″) phase to the planar zigzag (β) phase occurs via melting and recrystallization. Under specific conditions, the β-phase is metastable, even in its thermodynamically stable region.