Dialkylene carbonate-bridged polysilsesquioxanes. Hybrid organic-inorganicsol-gels with a thermally labile bridging group

In this paper, we introduce a new approach for altering the properties of b ridged polysilsesquioxane xerogels using postprocessing modification of the polymeric network. The bridging organic group contains latent functionalit ies that can be liberated thermally, photochemically, or chemically after t he gel has been processed to a xerogel. These modifications can produce cha nges in density, solubility, porosity, and or chemical properties of the ma terial. Since every monomer possesses two latent functional groups, the tec hnique allows for the introduction of high levels of functionality in hybri d organic-inorganic materials. Dialkylene carbonate-bridged polysilsesquiox ane gels were prepared by the sol-gel polymerization of bis(triethoxysilylp ropyl) carbonate (1) and bis(triethoxysilylisobutyl) carbonate (2). Thermal treatment of the resulting nonporous xerogels and aerogels at 300-350 degr ees C resulted in quantitative decarboxylation of the dialkylene carbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilse squioxane monolithic xerogels and aerogels that cannot be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.