Surface Segregation of a Star-Shaped Polyhedral Oligomeric Silsesquioxane in a Polymer Matrix

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 (3Ph-C3 and 3Ph-C6) by the hydrosilylation of heptaphenylallyl- and hexenyl-POSS (1a and 1b) and octadimethylsiloxy-Q8-silsesquioxane (Q8M8H) (2), respectively, and their properties were compared with those of the corresponding isobutyl-substituted derivatives (5iBu-C3 and 5iBu-C6). Although 3Ph-C6 was only soluble in chloroform and insoluble in tetrahydrofuran (THF) and toluene, 3Ph-C3 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 3Ph-C3 exhibited a baseline shift at 190 °C and an endothermic peak at 316 °C. However, no clear baseline shift was observed for 3Ph-C6. 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 3Ph-C3 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 3Ph-C6. Poly(methyl methacrylate) (PMMA) films containing 2 wt % 3Ph-C3 and 3Ph-C6 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 3Ph-C3 and 3Ph-C6 suggested that degree of the segregation amount of 3Ph-C3 was larger than that of 3Ph-C6. The shorter linker length in the phenyl-substituted star-shaped POSS derivative, 3Ph-C3, with its greater predicted solubility in PMMA, exhibited entropy-driven surface segregation.

Synthesis of a series of octaalkoxy-substituted cage silsesquioxanes catalyzed by zinc acetate

Octaalkoxy-substituted polyhedral oligomeric silsesquioxane (8RO-POSS) is an attractive starting material for producing silicone resins. However, polymers derived from 8RO-POSS via the sol-gel process have seldom been reported owing to their synthetic difficulty. In this study, we attempted to use zinc acetate (Zn(OAc)2) as the catalyst for the synthesis of a series of 8RO-POSS from octahydrido-POSS (8H-POSS). The reaction conditions were optimized using heptaisobutyl monohydride-POSS (7iBu1H-POSS) as a model reaction. The desired product was obtained in 96% yield under optimized conditions. The alkoxylation of 8H-POSS was performed using methanol (MeOH), ethanol (EtOH), isopropyl alcohol (i-PrOH), and tert-butyl alcohol (t-BuOH) in the presence of Zn(OAc)2 as the catalyst. Although octamethoxy-POSS (8MeO-POSS) was isolated in the presence of a byproduct, octaethoxy-POSS (8EtO-POSS) and octaisopropoxy-POSS (8iPrO-POSS) were obtained in high yields. The degree of alkoxylation was 55% in the case of using t-BuOH. The structures of 8MeO-POSS, 8EtO-POSS, and 8iPrO-POSS were confirmed by FT-IR, 1H-, and 29Si-NMR and MALDI-TOF-MS analyses. Compared to the random silicate obtained by base-treated tetramethoxysilane (TMOS), base-treated 8EtO-POSS and 8iPrO-POSS showed that the cage structures were maintained even after the formation of condensed silicate structures via a condensation reaction.

Hybrid polyurethanes composed of isobutyl-substituted open-cage silsesquioxane in the main chains: synthesis, properties and surface segregation in a polymer matrix

The resulting polyurethanes exhibited excellent optical transparency and surface hydrophobicity and acted as effective surface modifiers in poly(methyl methacrylate) (PMMA) by surface segregation.

SiO2/Ladder-Like Polysilsesquioxanes Nanocomposite Coatings: Playing with the Hybrid Interface for Tuning Thermal Properties and Wettability

The present study explores the exploitation of ladder-like polysilsesquioxanes (PSQs) bearing reactive functional groups in conjunction with SiO2 nanoparticles (NPs) to produce UV-curable nanocomposite coatings with increased hydrophobicity and good thermal resistance. In detail, a medium degree regular ladder-like structured poly (methacryloxypropyl) silsesquioxane (LPMASQ) and silica NPs, either naked or functionalized with a methacrylsilane (SiO2@TMMS), were blended and then irradiated in the form of a film. Material characterization evidenced significant modifications of the structural organization of the LPMASQ backbone and, in particular, a rearrangement of the silsesquioxane chains at the interface upon introduction of the functionalized silica NPs. This leads to remarkable thermal resistance and enhanced hydrophobic features in the final nanocomposite. The results suggest that the adopted strategy, in comparison with mostly difficult and expensive surface modification and structuring protocols, may provide tailored functional properties without modifying the surface roughness or the functionalities of silsesquioxanes, but simply tuning their interactions at the hybrid interface with silica fillers.