The membrane selection criteria for the preferential permeation of a particular component were examined for the pervaporative separation of methanol from a mixture of methanol and toluene. One polyacrylonitrile homopolymer and five different copolymer membranes (i.e., acrylonitrile with maleic anhydride, acrylic acid, methacrylic acid, methyl methacrylate, and styrene) were prepared through emulsion polymerization. All these monomers were selected on the basis of the solubility parameter concept. The second monomer had an influence on the permselectivity and flux, and this effect was investigated. The structures of the copolymers, the features of their sorption layers, and their permeation paths were examined. (C) 2005 Wiley Periodicals, Inc.