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 25 °C as well as at 150 °C to enhance the scattering contrast in order to obtain more reliable morphological parameters. The compression-molded sample was crystallized into a β′ 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 150 °C, provided that the appropriate subtraction of intensifies 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 25 °C was obtained and a comparison of the morphological parameters was provided as well.