Strong diffuse scattering and lamellar morphologies of syndiotactic polystyrene: Polymorphic effects

Syndiotactic polystyrene (sPS) samples melt-crystallized into neat alpha"- hexagonal and beta'-orthorhombic modifications were prepared at various temperatures thoroughly for extensive morphological studies. The lamellar morphologies of the as-prepared sPS samples were investigated with small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). For SAXS measured at 25degreesC, a barely observed scattering hump was detected for beta'-form sPS, whereas no discernible scattering feature was found for alpha"-form sPS because of a small difference in the electron density between the crystalline and amorphous phases. For increased scattering contrast and strength, SAXS was carried out at 150degreesC so that more reliable morphological parameters would be obtained. In addition to the enhanced scattering peak relevant to the lamellar features, strong diffuse scattering near the beam stop was observed for both alpha"- and beta'-form sPS samples. The contribution of the diffuse scattering at low q regions (where q is the scattering vector) was rather prominent, obscuring the precise position of the scattering peak. On the basis of the Debye-Bueche theory, the strength and inhomogeneity length were derived to render the diffuse scattering. After the subtraction of the diffuse scattering from the observed intensities, scattering intensities exclusively associated with the lamellar features were obtained. Lamellar thicknesses were further derived from the one-dimensional correlation function of the modified intensities, and a good agreement was reached in comparison with TEM results. From exhaustive TEM observations on the RuO4,-stained samples, long and parallel lamellae were readily observed in beta'-form sPS. However, relatively irregular packing of lamellar stacks with short lateral dimensions was detected in the as-prepared alpha"-form sPS, leading to the absence of spherulitic birefringence under polarized optical microscopy. (C) 2003 Wiley Periodicals, Inc.