Polyhedral oligosilsesquioxane (POSS) nanoparticle localization in ordered structures formed by solvated block copolymers

The coassembly of polyhedral oligosilsesquioxanes (POSS) of two different surface chemistries is considered, one hydrophilic, poly(ethylene oxide) (PEO), and the other hydrophobic, isobutyl (iB), in cylindrical structures formed by hydrated poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymer, Pluronic P105 (EO₃₇PO₅₆EO₃₇). Incorporation of PEO-POSS by replacing an equal mass of water results in an increase in the lattice parameter (d), which is attributed to an increase in the degree of block segregation. In the case of adding PEO-POSS at a fixed Pluronic P105/water ratio, d ~ φ_polymer^-0.7, which suggests that PEO-POSS particles are located inside the hydrated PEO domains. Incorporation of iB-POSS in the water-in-xylene cylindrical structure causes an order-to-order phase transition to a bicontinuous cubic structure, which suggests that iB-POSS decreases the degree of block segregation by locating at the PEO-PPO interfacial regions. The nanoparticle versus molecule nature of POSS is discussed by comparing POSS effects to those of 10.6 nm diameter deprotonated silica nanoparticles and of glycerol or glucose. Polyhedral oligosilsesquioxanes (POSS) can be viewed as small nanoparticles or large solvent molecules, and can thus impart diverse properties in POSS-containing nanocomposites. Coassembly of POSS with ordered block copolymers can modulate the phase behavior and structure (depending on the POSS amount and surface chemistry), with potential benefits in applications such as polymer composites and coatings.