Functional groups on POSS nanoparticles influence the self-assembled structures of diblock copolymer composites

We investigated the influence of the functional groups presented by polyhedral oligomeric silsesquioxane (POSS) nanoparticles (NPs) on the self-assembled structures formed by diblock copolymer composites. We blended two amorphous POSS derivatives, octakis[ dimethyl(4-phenethyl)siloxy]silsesquioxane (OS-POSS) and octakis[ dimethyl(4-hydroxyphenethyl)siloxy]silsesquioxane (OP-POSS), with the block copolymer poly(styrene-b-4-vinyl pyridine) (PS-b-P4VP). This long-range order transformed into distorted lamellar structures when we blended PS-b-P4VP with the OS-POSS NPs due to the relatively weak intermolecular hydrophobic forces between the aromatic groups of OS-POSS and the PS block segments. In contrast, we obtained well-defined self-assembled structures, in the form of block copolymer nanocomposites, after blending PS-b-P4VP with the OP-POSS NPs; an order-order morphological transition occurred upon increasing the content of OP-POSS NPs in the PS-b-P4VP diblock copolymer. Transmission electron microscopy and small-angle X-ray scattering revealed morphologies exhibiting high degrees of long-range order, namely lamellar structures at low OP-POSS NP contents, hexagonally packed cylindrical structures at higher OP-POSS NP contents, and a body-centered cubic spherical structure at the highest OP-POSS NP content, due to relatively strong hydrogen bonding interactions between the OH groups of the OP-POSS NPs and the pyridyl groups of the P4VP block segments.