Molecular engineering with bridged polysilsesquioxanes

Bridged polysilsesquioxanes are a class of hybrid organic-inorganic materials that permit molecular engineering of bulk properties including porosity. Prepared by sol-gel polymerization of monomers with two or more trialkoxysilyl groups, the materials are highly cross-linked amorphous polymers that are readily obtained as gels. The bridging configuration of the hydrocarbon group insures that network polymers are readily formed and that the organic functionality is homogeneously distributed throughout the polymeric scaffolding at the molecular level. This permits the bulk properties, including surface area, pore size, and dielectric constant to be engineered through the selection of the bridging organic group. Numerous bridging groups have been incorporated. This presentation will focus on the effects that the length, flexibility, and substitution geometry of the hydrocarbon bridging groups have on the properties of the resulting bridged polysilsesquioxanes. Details of the preparation, characterization, and some structure property relationships of these bridged polysilsesquioxanes will be given