Phenolic Functionality of Polyhedral Oligomeric Silsesquioxane Nanoparticles Affects Self-Assembly Supramolecular Structures of Block Copolymer Hybrid Complexes

We prepared polyhedral oligomeric silsesquioxane (POSS) nanoparticles (NPs) presenting one, two, and eight phenolic OH units (MP-POSS, BP-POSS, and OP-POSS, respectively) and investigated their blends with poly(styrene-b-4-vinylpyridine) (PS-b-P4VP) diblock copolymer. We prepared MP-POSS, BP-POSS, and OP-POSS each through a simple two-step synthesis including the hydrosilylation of 4-acetoxystyrene (AS) with H-POSS, DDSQ, and Q(8)M(8)(H), respectively, and then subsequent hydrolysis of acetoxyl groups with N2H4. Fourier transform infrared spectra and differential scanning calorimetry revealed that the hydrogen bonding strengths in the three hybrid complexes follow the order of P4VP/OP-POSS > P4VP/BP-POSS > P4VP/MP-POSS. Small-angle X-ray scattering and transmission electron microscopy revealed that the self-assembly nanostructures formed by PS-b-P4VP were strongly dependent on the nature of the POSS NPs. The weakly hydrogen bonded PS-b-P4VP/MP-POSS hybrid formed a disordered structure at MP-POSS contents greater than 10 wt %. The moderately hydrogen bonded PS-b-P4VP/BP-POSS hybrid self-assembled into structures ranging from lamellar to cylindrical upon increasing the BP-POSS concentration higher than SO wt %. The strongly hydrogen bonded PS-b-P4VP/OP-POSS hybrid underwent a full sequence of order order morphological transition-from lamellar, bicontinuous double gyroid, cylindrical, and finally to body-centered cubic spherical structures-with the increase of OP-POSS concentrations. The number of phenolic OH functionalities presented by the POSS NPs was the key factor affecting the nature of these self-assembled structures.