In this work, hybrid materials were synthesized as self-supported films from divinylbenzene and cyclic siloxane, in different compositions, by hydrosilylation reaction. These films showed good thermal and mechanical properties. Their glass transition temperatures were higher than those of conventional silicone networks, and dependent on divinylbenzene amounts. Films were homogeneous and no pores were observed by field emission electron scanning microscopy. Relationships between surface roughness and composition of the obtained films were discussed. The nanomorphology of the materials was studied by small angle X-ray scattering, showing polydispersed nano-sized heterogeneities. The gas permeability of the hybrid films was investigated, and the results suggested low permeable behaviour to gases, but high ideal selectivities to some pairs of gases, such as H-2/O-2. (C) 2003 Elsevier Ltd. All rights reserved.403615622