Conformationally Sensitive Infrared Vibrations of the Syndiotactic Polystyrene/Ethylbenzene Complex

The 920−960 cm -1 region of the infrared spectrum of the δ phase syndiotactic polystyrene/ethylbenzene predominantly involves bands arising from helical structures and has been studied here as a function of heating temperature. Curve fitting and deconvolution showed the necessity, for annealing temperatures above 120 °C, of adding a third component at 940 cm -1 to peaks at 934 and 943 cm -1 . The 934 and 943 cm -1 peaks behave as a doublet, primarily due to the δ phase, with the splitting increasing on annealing. The 940 cm -1 peak is solely due to the γ phase helix. Importantly, these assignments provide the opportunity for using these bands for further studies of complexation/decomplexation in such systems. The reduction in absorbance of 934 and 943 cm -1 peaks occurs at a lower temperature than the rise in the 940 cm -1 absorbance, and this is attributed to disordering of the δ phase helices prior to reformation as γ phase helices. Similar measurements using deuterated syndiotactic polystyrene also showed helix and zigzag bands, but without a predominantly δ phase helix peak. Solvent peaks in the deuterated syndiotactic polystyrene/ethylbenzene system were used to monitor the δ to γ phase transition. In combination with DSC and TGA data, the melting temperature of the α phase was found to be depressed by 7 °C for the deuterated polymer, while the δ to γ phase transition temperature was shown to be around 24 °C higher.