Poly(vinyl acetal) PVAc was synthesized by the acid-catalyzed acetalisation of poly(vinyl alcohol). Three different morphologically modified variants of the polymer were prepared by the addition of supramolecules; namely alpha and beta cyclodextrins (CD) and butyl calixerene (calix) to the PVAc sol. 20% (w/v) of the solution of the polymers in tetrahydrofuran (THF) was used to cast the membranes. These membranes were characterized using spectroscopic and thermoanalytical techniques, and also tested for their chemical resistance and mechanical strength. The pervaporative behaviour of modified membranes vis-a-vis PVAc for the separation of a wide composition of benzene (Bz)/cyclohexane (Chx) mixtures was evaluated. Addition of alpha CD or calix to PVAc reduced the overall flux while dispersion of beta CD favoured an enhanced flux especially in the Bz-lean and azeotropic region. (C) 2005 Elsevier B.V. All rights reserved.