The pervaporation (PV) performance of partly hydrolyzed poly(vinyl acetate) (PHPVAC) membranes in benzene/cyclohexane separaion was examined. The extremum and asymmetric changes of PV performance, the separation factor (alpha) and the permeation flux (J) of PHPVAC membrane with cast solvent composition (water/dioxane, H2O/DIO) were observed. Also, the dilute solution behavior of PHPVAC in H2O/DIO was investigated. The maximum of intrinsic viscosity [eta], the minimums of Huggins constant k(H), flow active energy E-eta, and asymmetric changes with the solvent composition also occurred. Both extreme phenomena for both PV performance of PHPVAC membranes and the solution behavior of PHPVAC could be explained by the conformational transition of amphiphilic PHPVAC in the selective solvent mixtures. (c) 2005 Elsevier B.V. All rights reserved.