Reactive microgels (RM) were prepared by the copolymerization of styrene and an unsaturated polyester in an emulsion of oil (styrene + unsaturated polyester) in water. The adsorption of the unsaturated polyester on the water-oil interface ensured the stability of the emulsion. Furthermore, polyacrylamide (PAAM) crosslinked with RM was obtained by suspending RM particles in an aqueous AAM solution and polymerizing the system at 70 degrees C to obtain a PAAM-RM composite. The extraction experiments of the RM with dioxane and of the PAAM with water indicated the presence of small amounts of soluble PAAM homopolymers and negligible amounts of free RM, the materials being PAAM crosslinked by RM. The extent of swelling of these materials in water decreased with increasing weight ratio of RM/AAM and was independent of the composition of RM. When the final poly merization temperature was increased to 130 degrees C, RM reacted not only with AAM to form a crosslinked polymer, but also with itself to form semi-interpenetrating reactive polymer networks (SIRPN). The extent of swelling of PAAM-RM SIRPN in water was much lower than that of the PAAM-RM material. Membranes were also prepared by hot pressing at 200 degrees C the PAAM-RM and PAAM-RM SIRPN composites. The swelling behavior of these membranes in water, acetone, tetrahydrofuran, acrylic acid, ethyl alcohol, and dioxane, as well as in the mixtures of ethyl alcohol-water, acetone-water, tetrahydrofuran-water, and acrylic acid-water, was investigated.