Phenyl-Substituted Cage Silsesquioxane-Based Star-Shaped Giant Molecular Clusters: Synthesis, Properties, and Surface Segregation Behavior.

The crystallinity, solubility, and physical properties of polyhedral oligomeric silsesquioxane (POSS) compounds are highly dependent on their organic substituents. We previously synthesized a series of isobutyl-substituted star-shaped POSS derivatives with aliphatic chain linkers of different length. In this study, we prepared C3- and C6-linked phenyl-substituted star-shaped POSS derivatives ( and ) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS ( and ) and octadimethylsiloxy-Q-silsesquioxane (QM) (), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives ( and ). Although was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, was soluble even in THF and toluene, suggesting that the shorter linkers of the derivative afford a wider range of solvents for dissolution. Differential scanning calorimetry analysis showed that exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for . Thermogravimetric analysis showed that the shorter linker in the phenyl-substituted star-shaped POSS derivative significantly increased the decomposition temperature compared with the longer linker. The annealed cast film of at 340 °C above its melting temperature formed a transparent film even after cooling to room temperature. However, an opaque whitish film was formed in the case of . Poly(methyl methacrylate) (PMMA) films containing 2 wt % and were prepared by casting their chloroform solutions onto glass substrates overnight at room temperature. The static water contact angle measurements and XPS analysis for the castings film containing and suggested that degree of the segregation amount of was larger than that of . The shorter linker length in the phenyl-substituted star-shaped POSS derivative, , with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.