Molecular aggregation structure and properties of silsesquioxane-terminated polystyrene

Organic-inorganic hybrid polymers (PS-POSS), which are polystyrene (PS) with polyhedral oligomeric silsesquioxane (POSS) end group, were prepared by nitroxide-mediated radical polymerization. PS-POSS thin films were spin-coated from its toluene solution onto acid-cleaned silicon wafers. After annealing at 393 K for 3 h, PS-POSS (M_n=2500, M_w/M_n=1.11; PS-POSS2.5k) thin film did not dewet at all, in contrast, the bare substrate was observed as a consequence of the complete dewetting of the pure PS (M _n=2100, M_w/M_n=1.06; PS2.1k) film. Differential scanning calorimetric analysis showed that the glass transition temperature of PS-POSS2.5k was 348.1 K, which means a noticeable increase from that of PS2.1k. Rheological characterization of PS-POSS2.5k suggested that the introduction of POSS as the chain end group of PS delays the dynamics of the polymer chain in melt state. Furthermore, neutron reflectivity measurement revealed that the POSS moiety of PS-POSS formed enriched layer at the surface and interface of the film. The segregation of POSS, which changes the surface and interface free energy of the film, can be an important factor in the dewetting inhibition effect.