AB-type monomer of polyhedral oligomeric silsesquioxane

Polyhedral oligomeric silsesquioxanes (POSSs) are crucial building blocks for the fabrication of organic–inorganic hybrid materials. Bifunctional POSS monomers have been developed using incompletely condensed POSS (IC-POSS) for main-chain-type POSS polymers. The existing IC-POSS monomers are predominantly A₂-type and AB-type IC-POSS monomers have not been reported to date. In this study, we introduced a strategy for synthesizing an AB-type POSS monomer. Commercially available corner-opened POSS trisilanol was transformed into an AB-type monomer endowed with vinyl and hydrosilyl groups via sequential condensation with dichloromethylvinylsilane and chlorodimethylsilane. The resulting product yielded a mixture of isomers, one with the vinyl group oriented outward and the other oriented inward relative to the cage core. Pt-catalyzed hydrosilylation of the former isomer generated a polymer, whereas the latter produced a cyclic compound. A structurally controlled polymer was selectively synthesized from the isomeric mixture of AB-type monomers.