Syndiotactic polystyrene (sPS) has been found to exhibit two distinct vibrational peaks in the Raman spectrum corresponding to the ν1 vibrational mode. These features have been assigned to the symmetric phenyl ring breathing mode coupled to the polymer backbone. It has been shown that the presence of long all-trans sequences gives rise to a peak at ∼773 cm-1, whereas less well-defined trans/gauche conformations result in a separate peak at ∼798 cm-1. With increasing levels of crystallinity, the integrated intensity of the former feature grows at the expense of the high-frequency feature. The use of a series of annealed isotropic films of glassy sPS of increasing crystallinity and molten sPS has made it possible to examine the precise relationship between these two features and other neighboring vibrational peaks. The level of crystallinity within each sample has been determined independently using wide-angle X-ray scattering, differential scanning calorimetry, and infrared spectroscopic measurements. It has been found that the relative area under the all-trans ν1 band can be directly related to the crystalline volume fraction within each sample. It is proposed that this Raman vibrational feature centered around 773 cm-1 can be used as a quantitative measure of crystallinity for sPS once the contribution from the all-trans sequences in the melt is subtracted from the spectrum.
The structure and morphology of syndiotactic polystyrene (sPS) injection molded coupons have been investigated using wide angle X-ray scattering (WAXS), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), light microscopy, and laser Raman spectroscopy (LRS). By sectioning the samples at approximately 200 pm increments, profiles across "hot molded (oil heated to 140°C) and "cold molded" (water heated to 104°C) coupons, could be built up. Using DSC and WAXS, variations in crystallinity and polymorphic phases were observed. The crystallinity was found to remain fairly constant in the "hot molded" samples, whereas the cold molded samples had a pronounced "amorphous" skin, before becoming more uniform towards the center of the specimen. Characterization of the polymers' microstructure, in the molded plaques, was achieved by optical birefringence. The surface of the plaques were successfully etched with an acid/permanganate solution, prior to SEM studies, to reveal their morphology. Overall, the coupons showed very little orientation effects and the structure appeared to be consistent with that of a semicrystalline polymer, crystallized under relaxed conditions.
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