Composite membranes have been prepared starting from concentrated emulsions of styrene in aqueous solutions of acrylic acid as precursors. Each of the phases of the emulsion contained a suitable initiator and the continuous phase contained a dispersant (sodium dodecylsulfate). The polymerization of the precursor generated a composite consisting of particles of dispersed phase imbedded in the continuous phase. To obtain the membranes, the polymer powders generated via grinding were subjected to hot pressing. The mechanical properties of the membranes have been improved by dissolving either butyl acrylate or styrene-butadiene-styrene three block copolymer in styrene. The membranes have been used to separate benzene from benzene-cyclohexane mixtures. The components of the membranes have been selected because polystyrene swells well in benzene and much less in cyclohexane, while the poly(acrylic acid) does not swell well in either of the components and can, therefore, maintain the integrity of the membrane. The mechanical and sorption behaviors of the membranes as well as their pervaporation capabilities were investigated.