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

Abstract

The empty δ (δe) form of uniaxially oriented syndiotactic polystyrene (sPS) was obtained by extracting the solvent molecules from the δ form of the sPS−solvent complex in acetone and methanol. The X-ray fiber diagrams of the δe 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 δe form at various temperatures for the first time. It has been found that the δe form transforms to the intermediate form transiently before transforming into the γ form. Temperature-dependent polarized FTIR spectra were measured also for the uniaxially oriented δe sample derived from the sPS and chloroform complex. The infrared band intensity characteristic of the T2G2 conformation was found to change drastically in the course of transition from the δe to the intermediate phase and to the γ 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 δe 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 δe, intermediate, and γ forms.