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

In this paper, the authors introduce a new approach for altering the properties of bridged polysilsesquioxane xerogels using postprocessing modification of the polymeric network. The bridging organic group contains latent functionalities that can be liberated thermally, photochemically, or chemically after the gel has been processed to a xerogel. These modifications can produce changes in density, solubility, porosity, and or chemical properties of the material. Since every monomer possesses two latent functional groups, the technique allows for the introduction of high levels of functionality in hybrid organic-inorganic materials. Dialkylene carbonate-bridged polysilsesquioxane gels were prepared by the sol-gel polymerization of bis(triethoxysilylpropyl) carbonate and bis(triethoxysilylisobutyl) carbonate. Thermal treatment of the resulting nonporous xerogels and aerogels at 300--350 C resulted in quantitative decarboxylation of the dialkylene carbonate bridging groups to give new hydroxyalkyl and olefinic substituted polysilsesquioxane monolithic xerogels and aerogels that cannot be directly prepared through direct sol-gel polymerization of organotrialkoxysilanes.