SynopsisDirect determination of the Flory-Huggins interaction parameter x of a polymer blend by small-angle x-ray scattering experiments is possible on the basis of the random phase approximation, if absolute intensities are measured. The usually superposed void scattering has to be properly accounted for. Investigations on a series of blends of polystyrene and poly(styrene-cobromostyrene) yielded x dependent upon the blend composition. x shows only slight variations.Scattering data also give the radii of gyration of the two components in the blend.

Depolarized light scattering has been applied to study the anisotropy fluctuations in a series of polystyrenelpolyisoprene diblock copolymers. This method is selective for the dynamica of the polystyrene block. The molecular weights of the block copolymers (10500-20800) were chosen such that the microphase separation transition (MST) occurs at temperatures which are experimentally acceeeible with photon correlation spectroscopy. Small-angle X-ray scattering (SAXS) was used to identify the disordered regime, the fluctuationcontrolled transition regime, and the ordered state. The relaxation time spectrum in the disordered state is similar to that of bulk polystyrene. Concentration fluctuations increasingly broaden the spectrum and lead to a bimodal shape. Close to the MST the spectrum becomes dominated by a slow, nearly single exponential contribution. Comparison with the SAXS results suggests that this splitting of the relaxation time spectrum can be related to chain stretching.

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Static and dynamic light scattering was applied in a comprehensive study of the different modes of relaxatory motion in polystyrene-dioxane mixtures, comprising the whole range of different compositions from dilute solution to plasticized melts. For the analysis of data measured in the presence of the nearly elastic anomalous excess scattering usually encountered in concentrated solutions and the melt, a generalized Siegert relation was used. Analysis of depolarized dynamic scattering data obtained for the PS-rich mixtures indicates a simple Vogel-Fulcher temperature dependence for the relaxation rates of the anisotropy fluctuations with T¡ as the only relevant parameter. The dynamics observed in polarized scattering continuously changes its character, being dominated at low temperatures and high concentrations by density fluctuations and in the limit of high temperatures and low concentrations by concentration fluctuations.Density and anisotropy fluctuations show identical relaxation rates.

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