Viscoelastic properties of POSS-styrene nanocomposite blended with polystyrene

Polyhedral oligomeric silsesquioxane (POSS) are hybrid nanostructures of about 1.5 nm in size. These silicon (Si)-based polyhedral nanostructures are attached to a polystyrene (PS) backbone to produce a polymer nanocomposite (POSS-styrene). We have solution blended POSS-styrene of (M) over bar (w) = 14.5 x 10(3) g/mol with commercial polystyrene (PS), (M) over bar (w) = 2.8 x 10(5) g/mol, and studied the rheological behavior and thermal properties of the neat polymeric components and their blends. The concentration of POSS-styrene was varied from 3 up to 20 wt.%. Thermal analysis studies suggest phase miscibility between POSS-styrene and the PS matrix. The blends displayed linear viscoelastic regime and the time-temperature superposition principle applied to all blends. The flow activation energy of the blends decreased gradually with respect to the matrix as the POSS-styrene concentration increased. Strikingly, it was found that POSS-styrene promoted a monotonic decrease of zero-shear rate viscosity, eta(0), as the concentration increased. Rheological data analyses showed that the POSS-styrene increased the fractional free volume and decreased the entanglement molecular weight in the blends. In contrast, blending the commercial PS with a PS of (M) over bar (w) = 5 x 10(3) g/mol did not show the same lubrication effect as POSS-styrene. Therefore, it is suggested that POSS particles are responsible for the monotonic reduction of zero-shear rate viscosity in the blends.