A series of hydrogenous and deuterated four-arm polystyrene stars with low polydispersity have been synthesized by anionic polymerization. Self-diffusion data have been obtained using helium-3 nuclear reaction analysis, and rheology has been employed to obtain the zero shear viscosity. Both diffusion and viscosity data have been compared to results predicted by recent theories in order to test the alternative models of diffusion cases, i.e., arm retraction followed by the core hopping either a diluted or an undiluted tube diameter. The exponential dependence on molecular weight can be conveniently removed by taking the product of the self-diffusion and the viscosity, making it possible to determine which model is more appropriate. Our data show good agreement with the undiluted tube model over a range 3.5 > N/N e < 9. At low molecular weight the data show the model failing at N/N e < 3, in agreement with theoretical predictions.

Polymer/clay nanocomposites (PCNs) of poly(methyl methacrylate) and an organically modified clay, Cloisite 15a, were synthesized in situ with a suspension polymerization technique. The amount of clay present in the PCNs was varied to provide a better understanding of the effect of the clay on the properties of the polymer matrix. However, unexpectedly, we found that the concentration of clay had a dramatic impact on the molecular weight of the polymer matrix, and a relationship between the clay concentration and polymer molecular weight was determined. The PCNs were characterized with size exclusion chromatography (SEC), X-ray diffraction, transmission electron microscopy, and oscillatory shear rheology.From oscillatory shear rheology, the full master curves for the PCNs were obtained by application of the time-temperature superposition principle. To enable the effect of the clay on the rheology to be quantified, the experimental data was compared to the time-dependent diffusion model of des Cloizeaux for polydisperse polymer melts, which enabled the polydispersity to be incorporated through the use of the molecular weight distribution obtained via SEC.

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The melt rheology of blends of a low molar mass liquid crystal (LC) blended with bisphenol A-polycarbonate (PC), and the self-diffusion of the polycarbonate in the blends are reported. Results of small angle light scattering indicate that the LC is miscible in the mixture for weight fraction of LC less than 6%. The rheological properties of the blended sample within the miscible regime of the blends vary significantly with LC content. Although at low shear rates, the viscosity is similar to that of the pure polycarbonate, at high shear rates the curves show three regions of behavior, as has been described previously for pure LCs. The diffusion coefficient was obtained from interdiffusion studies using nuclear reaction analysis of bilayer films. An addition of only 1 wt % LC to the polycarbonate significantly increased the diffusion coefficient, but at higher concentration the converse was found.