alpha,omega-Dihydroxy-polydimethylsiloxane (PDMS)/poly(methyl methacrylate) (PMMA) blends were prepared by the radical polymerization of methyl rnethacrylate in the presence of PDM, with benzoyl peroxide as the initiator. The PDMS/PMMA blends obtained by this method were a series of stable, white gums, which were vulcanized into elastomers at room temperature with methyl triethoxysilicane (MTES). The MTES dosage was much larger than the amount necessary for end-linking the hydroxy-terminated chains of PDMS, with the excess being hydrolyzed into crosslinked networks, which were similar to Sib, and acted as fillers. Investigations were carried out on the elastomeric materials by extraction measurements, swelling measurements, and scanning electron microscopy. The extraction data showed that at each composition, the sol fraction was less than expected. The extracted materials were further studied with swelling measurements, which revealed that the material obtained from an elastomer with a higher PMMA content had an apparently larger equilibrium swelling degree. Scanning electron microscopy demonstrated that the elastomer system had a microphase-separated structure consisting of PMMA domains within a continuous PDMS matrix. Moreover, the mechanical properties of the elastomeric materials were studied in detail. (c) 2006 Wiley, Periodicals, Inc.