Separation and transport properties of AB membranes during pervaporation of water-methyl acetate (water-MeAc) and water-methyl tert-butyl ether (water-MTBE) mixtures were investigated. Membranes were prepared from AB-crosslinked copolymer composed of elastomeric oligo or poly H-polysiloxanes and glassy styrene/isoprene prepolymer. Results showed that the properties depended on the siloxane content in the membrane. The pervaporation properties of AB membranes were much better than properties of the commercially available hydrophobic membranes. The percolation threshold of permeability and selectivity was observed for AB membranes containing 35-40 wt.% of siloxane. (C) 2003 Elsevier Science B.V. All rights reserved.