Polymer−Solvent Interactions in Crystalline δ Form of Syndiotactic Polystyrene Viewed from the Solvent-Exchange Process in the δ Form and the Solvent Evaporation Phenomenon in the Thermally Induced δ−γ Phase Transition

The δ form, one of various crystalline forms of syndiotactic polystyrene (sPS), is a complex between sPS and solvent molecules. This crystalline form shows a solvent exchange between the originally absorbed solvent B and the newly supplied solvent A when the δ form sample was exposed to the solvent A atmosphere. We have carried out the time-resolved infrared spectral measurement during this solvent-exchange process and found that the solvent-exchange rate was almost common to any pair of solvents where the solvents A and B were toluene, chloroform, or benzene. On the other hand, when the δ form sample was heated above 150 °C, it transferred to the γ form having no solvent molecules in the crystal lattice. The temperature, where most of solvent molecules were evaporated from the sample, was almost common to any kind of solvent originally absorbed in the δ form, as already pointed out by Gowd et al. [Macromolecules 2002, 35, 8509]. All these phenomena, i.e., the solvent-exchange phenomenon and the solvent evaporation phenomenon, were considered to come from the characteristic features of δ form crystal: the unique columnar structure and the relatively weak interactions between sPS chains and solvent molecules; the solvent molecules are trapped in the columns made by aggregated sPS chain stems. The solvent exchange was speculated to occur easily along the column axis. The evaporation of solvent in the δ-to-γ phase transition was considered to occur also along the column axis, and therefore almost no difference was observed for the different solvent system. When acetone was supplied to the δ form in the solvent-exchange experiment, the solvent originally trapped in the δ form was displaced by acetone molecules. But the original column structure was not affected by such a solvent exchangedifferent from the cases of other such solvent as toluene, benzene, or chloroform. The structure changed from δ to δe (empty δ) form for the first time when acetone evaporated from the sample at room temperature.