Crystal Structures of Syndiotactic Polymethoxystyrene–Solvent Complexes Derived by X‑ray Diffraction Data Analysis and Computer Simulation

Syndiotactic polymethoxystyrene (OMe-SPS) is one of the derivatives of industrially- important syndiotactic polystyrene (SPS). The polar methoxy (OMe) groups substituted on the phenyl rings of SPS chains remarkably increase the solubility of SPS in the organic solvents. The solubility was found to change depending on the substitution position of the OMe units. In the cases of the para- and ortho-substitutions of OMe groups, such organic solvents as tetrahydrofuran (THF) and toluene (TOL) dissolve the polymer quite easily even at room temperature. On the other hand, the meta-substituted OMe units were found to form the crystalline complexes (δ form) between the polymers and solvents (THF and TOL) by exposing the original β-crystalline form in the solvent vapor atmosphere at room temperature. That is, different from the case of SPS, the solvent-induced β-to-δ phase transition was found to occur by the introduction of OMe side groups. The washing of these complexes with boiling methanol purges the solvent molecules from the complexes to result in the production of the so-called γ form. The X-ray diffraction data were analyzed quantitatively by the combination with the energy optimization technique so that stereochemically reasonable structure models were obtained, which reproduced the observed diffraction data relatively nicely. The structural relation between these complexes and the γ form has been discussed concretely.