Viscoelastic properties of PS-POSS hybrid materials prepared by reactive processing

The viscoelastic properties of hybrid nanocomposites of polystyrene and polyhedral oligomeric silsesquioxane (PS-POSS) are determined in the molten state by small-amplitude oscillatory shear rheometry (SAOS) and in the solid state by dynamical-mechanical thermal analysis (DMA). PS-POSS samples synthesized to form various molecular structures and phase morphologies are investigated. Overall, both viscoelastic data sets correlate well with the POSS dispersion level and with the degree of grafting of the PS-POSS samples. From the SAOS data, enhanced POSS dispersion and degrees of grafting are characterized by deviations of the zero-frequency viscosity ratios of the Einstein and Einstein-Batchelor models and by linearity in the Han plots. PS-POSS samples with enhanced POSS dispersion and degrees of grafting are characterized as those with higher free-volume fractions and lower flow activation energies, as determined by storage modulus master curves that stem from applying the time-temperature superposition (TTS) principle to the DMA data.