alpha,omega-Dihydroxy-polydimethylsiloxane/polystyrene (PDMS/PS) blends were prepared by the solution polymerization of styrene (St) in the presence of alpha,omega-dihydroxy-polydimethylsiloxane (PDMS), using toluene as solvent and benzoyl peroxide (BPO) as initiator. The PDMS/PS blends obtained by this method are a series of stable, white gums, which were vulcanized to elastomers at room temperature with methyl-triethoxysilicane (MTES). The use level of MTES was far more than the necessary amount used to end-link hydroxy-terminated chains of PDMS, with the excess being hydrolyzed to crosslinked networks, which were similar to SiO2 and acted as filler. Investigations were carried out on the elastomeric materials by extraction measurement, swelling measurement, and scanning electron microscopy. The extraction data show that at each composition the amount of soluble fraction is less than expected and the difference between experimental and theoretical values becomes more and more significant as PS content increases. This is mainly due to the grafting of PS onto PDMS and the entanglement of PS in the interpenetrating polymer network (IPN), which consists of either directly linked PDMS chains or chains linked via PS grafts and is formed by free radical crosslinking of PDMS during the radical polymerization of St. PS grafted on PDMS is insoluble and PS entangled in the IPN is difficult to extract. Both render the soluble fraction to be less than expected. As the St content in preparing PDMS/PS blends increases, the probability of grafting PS onto PDMS, also increases, which may subsequently produce a higher crosslinking level of PDMS networks that linked via PS grafts by radical crosslinking. As a result, not only the amount of insoluble PS increases but also PS entangled in the IPN is more difficult to extract. Scanning electron microscopy demonstrates that the elastomer system has a microphase-separated structure and a certain amount of PS remains in the PDMS networks after extraction, which is in accordance with the extraction data. Moreover, the mechanical properties of the elastormeric materials have been studied in detail. (C) 2004 Wiley Periodicals, Inc.