Composite membranes of polystyrene (PS) together with a hydrophilic polymer were prepared via the concentrated emulsion polymerization method developed in this laboratory. In the concentrated emulsion precursor, styrene containing some styrene-butadiene-styrene three block copolymer (SBS) constituted the dispersed phase and a solution of a hydrophilic monomer in water the continuous phase. The polymerized systems were transformed in membranes by hot pressing at 150 degrees C. The mechanical properties of the membranes were affected by the amount of SBS in the dispersed phase and by the nature of the hydrophilic monomer of the continuous phase. SBS improved in a major way the mechanical properties of the membrane. The membranes were subjected to the sorption and pervaporation of benzene-ethanol mixtures. They exhibited preferential sorption toward benzene over the entire benzene concentration range, the swelling ratio increasing with increasing benzene concentration and the sorption selectivity decreasing. The prepared membranes had permeation rates as large as 1040 g/m(2)h and separation factors as large as 25 for the benzene-ethanol mixtures.