Highly porous elastomeric nanocomposites were successfully synthesized through copolymerization of 2-ethylhexyl acrylate (EHA), divinyl benzene (DVB), and up to 9 mol % of a polyhedral oligomeric silsesquioxane bearing one propylmethacryl group and seven cyclohexyl groups (MACH-POSS) within the external phase of high internal phase emulsions (HIPE). The chemical structures, morphologies, thermal properties, and mechanical properties of the polyHIPE were investigated. The mechanical loss peak temperature and full width at half maximum increased with increasing MACH-POSS content. These changes indicate that copolymerization with MACH-POSS limits segmental mobility and produces compositional distributions on the nanometer scale. At 9 mol % MACH-POSS, the reduction in segmental mobility produced a glass transition temperature above room temperature and a significant increase in modulus that can be ascribed to the relatively glassy nature of the polymer. Inorganic monoliths with porosities of around 86%, O/Si of about 1.6, and less than 10% carbon were produced on pyrolysis of the nanocomposite polyHIPE. (C) 2008 Wiley Periodicals, Inc.