Lamellar thickness of a syndiotactic polystyrene determined from small-angle X-ray scattering and transmission electron microscopy

Extensive morphological studies on a syndiotactic polystyrene (sPS) sample prepared from compression molding were carried out using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). SAXS was conducted at 25degreesC as well as at 150degreesC to enhance the scattering contrast in order to obtain more reliable morphological parameters. The compression-molded sample was crystallized into a beta' orthorhombic crystal lattice characterized by wide-angle X-ray diffraction (WAXD). A similar weight fraction of crystallinity, ca. 0.37, was obtained from both WAXD and differential scanning calorimetry measurements. In addition to the scattering peak at a scattering vector of ca. 0.36 nm(-1) attributable to the presence of lamellar/amorphous layers, anomalous scattering at the zero angle was found from the SAXS intensity profiles. Based on the Debye-Bueche theory, the scattering profile of this peculiar zero-angle scattering was deduced and was subtracted from the raw intensity profile to obtain the intensity profile exclusively associated with the lamellar/amorphous structure. A consistent long period was obtained for SAXS measured either at 25 or 150degreesC, provided that the appropriate subtraction of intensities due to the zero-angle scattering was conducted. Moreover, the lamellar thickness deduced from the one-dimensional correlation function was in good agreement with TEM results. A "difference scattering" pattern derived from SAXS measured at 150 and 25degreesC was obtained and a comparison of the morphological parameters was provided as well.