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

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 (3 and 3) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q₈-silsesquioxane (Q₈M₈^H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5 and 5). Although 3 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3 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 3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3. 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 3 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 3. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3 and 3 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 3 and 3 suggested that degree of the segregation amount of 3 was larger than that of 3. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.