Conformationally sensitive infrared vibrations of the syndiotactic polystyrene/ethylbenzene complex

The 920-960 cm(-1) region of the infrared spectrum of the delta 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 degrees 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 delta phase, with the splitting increasing on annealing. The 940 cm(-1) peak is solely due to the gamma 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 delta phase helices prior to reformation as gamma phase helices. Similar measurements using deuterated syndiotactic polystyrene also showed helix and zigzag bands, but without a predominantly delta phase helix peak. Solvent peaks in the deuterated syndiotactic polystyrene/ethylbenzene system were used to monitor the delta to gamma phase transition. In combination with DSC and TGA data, the melting temperature of the alpha phase was found to be depressed by 7 degrees C for the deuterated polymer, while the delta to gamma phase transition temperature was shown to be around 24 degrees C higher.