Molecular miscibility and chain dynamics in POSS/polystyrene blends: Control of POSS preferential dispersion states

Polyhedral oligomeric silsesquioxane (POSS)/polystyrene nanocomposites with two different POSS molecules, octaisobutyl POSS (Oib-POSS) and trisilanolphenyl POSS (Tsp-POSS), were prepared via solution blending in toluene. Solution dynamics analysis indicates random coil conformation of neat PS and POSS/PS blends. Morphology analysis (AFM/TEM) revealed differences in the preferential dispersion states of Tsp- and Oib-POSS molecules. Tsp-POSS, with its greater predicted solubility in PS, exhibited nanoscale dispersion throughout the bulk leading to transparent films. In contrast, Oib-POSS, with its reduced predicted solubility in PS, exhibited preferential surface segregation, aggregation of POSS particles and hazy films. Estimated fractional surface coverage for the materials, based on surface energy measurements, indicated 15% coverage by Tsp-POSS and 78% for Oib-POSS. Solid-state NMR relaxation studies suggest aggregation of Oib-POSS molecules. Additional NMR studies, including silicon CP/MAS, 2D HETCOR, and WISE, indicate close spatial proximity and interaction of Tsp-POSS molecules with PS chains, contrasting with poor interaction and immiscibility of Oib-POSS with PS.