A new kind of terpolymer membrane was employed to separate a permselective water-alcohol mixture. This membrane was prepared via the copolymerization of acrylonitrile, sodium salt styrene sulfonic acid (SStSA), and hydroxyethyl methacrylate in dimethylsulfoxide with azobisisobutyronitrile as an initiator. The reaction mechanism, resultant structure, and polymer composition were confirmed by IR and elemental analysis. The effects of the feed composition on the polymer composition, mechanical properties, thermal properties, and degree of swelling were investigated. It was found that water permeated through the membrane preferentially in a water/alcohol system. The flux increased with the increase of SStSA, but the separation factor decreased drastically with higher SStSA. For a 50 wt % water-ethanol mixture, a flux of 0.65 kg/m(2) h and a separation factor of 212 were obtained at 30degreesC when the membrane containing the highest SStSA content was used. The capacities of the metal ions absorbed by the membranes were investigated in the study. (C) 2003 Wiley Periodicals, Inc.