Structural changes in thermally induced phase transitions of uniaxially oriented δe form of syndiotactic polystyrene investigated by temperature-dependent measurements of X-ray fiber diagrams and polarized infrared spectra

The empty delta (delta(e)) form of uniaxially oriented syndiotactic polystyrene ( sPS) was obtained by extracting the solvent molecules from the delta form of the sPS-solvent complex in acetone and methanol. The X-ray fiber diagrams of the delta(e) form of different solvents like chloroform, toluene, and benzene were found to be appreciably different from each other, probably reflecting the difference in the cavity size after solvent evaporation. Temperature dependence of the X-ray fiber diagram has been measured successfully starting from the uniaxially oriented delta(e) form at various temperatures for the first time. It has been found that the delta(e) form transforms to the intermediate form transiently before transforming into the gamma form. Temperature- dependent polarized FTIR spectra were measured also for the uniaxially oriented delta(e) sample derived from the sPS and chloroform complex. The infrared band intensity characteristic of the T(2)G(2) conformation was found to change drastically in the course of transition from the delta(e) to the intermediate phase and to the gamma phase. On the basis of the X-ray diffraction profile and infrared spectra, the intermediate form is speculated to take the structure of disordered chain packing probably due to the empty cavities present in the original delta(e) form. Thermal data showing an endotherm followed by an exotherm during the transition can be interpreted reasonably using such order-to-disorder-to-order transitions among the delta(e), intermediate, and gamma forms.