Surface segregation of small amounts of additives in a polymer matrix is the most convenient and low-cost method to modify surface properties and functions. Although the surface segregation approach can increase the hydrophobicity of polymer surfaces, it is still a challenge to make the surfaces hydrophilic in an equivalent method. Here, we demonstrated that segregation of octa(dimethylsilylhydroxyethoxypropyl)silicate (OS-EGMAE), as a hydrophilic siloxane-based cage compound, occurred on the surface and at the interface of poly(methyl methacrylate) (PMMA) casting films without assistance of contacting high-free energy media. Addition of small amounts of OS-EGMAE in PMMA significantly enhanced wettability, and the lowest static contact angle of water of 28.9 ± 0.5°was observed for the cast film containing 4 wt % OS-EGMAE. The surface segregation of OS-EGMAE was confirmed by X-ray photoelectron spectroscopy. These findings clearly suggest that the siloxane-based cage frameworks are promising candidates for promoting surface segregation because of their predominantly contributed entropy factor to the total free energy.

Dumbbell-shaped polyhedral oligomeric silsesquioxane (POSS) derivatives, in which two POSS units are linked through a bridge, have attracted attention in the last decade. Here, we prepared an unsymmetric dumbbell-shaped POSS derivative (3 Ph-iBu ) in which isobutyl-and phenyl-substituted POSS units are linked by a disiloxane unit and compared its thermal properties with those of the corresponding symmetric isobutyl-and phenyl-substituted dumbbell-shaped POSS derivatives (3 iBu-iBu and 3 Ph-Ph , respectively). The symmetric isobutyland phenyl-substituted dumbbell-shaped POSS derivatives, 3 iBu-iBu and 3 Ph-Ph , were almost completely phase-separated during a mixing process. This phase separation is due to the limited solubility of phenyl-substituted POSS compounds, which are only soluble in tetrahydrofuran (THF) and insoluble in hydrocarbons such as n-hexane and toluene, while the isobutyl-substituted POSS derivatives exhibit a wider spectrum of soluble solvents. The unsymmetric dumbbell-shaped POSS, 3 Ph-iBu , showed hybrid properties of solubility in solvents and thermal behaviors. Differential scanning calorimetric (DSC) analysis showed that enthalpy of the phase transition of 3 Ph-iBu was significantly lower than those of the mixture of 3 iBu-iBu and 3 Ph-Ph . No apparent melting behavior was observed above the phase transition. The thermal degradation of the weakest isobutyl substituents improves in the present single-component hybrid structure.