Poly(vinyl alcohol) (PVA) was chemically modified by acid-catalysed acetalisation, resulting in the formation of poly(vinyl acetal) (PVAc). The addition of a molecular recognition compound, namely, O,O-bis(diethoxyphosphoryl)-tert-butyl calixarene (calix) to the PVA sol, yielded the morphologically modified membranes, designated as PVA-calix. These membranes were characterised using spectroscopic and thermoanalytical techniques, and also tested for their chemical resistance, mechanical strength and pervaporative behaviour towards benzene (Bz)/cyclohexane (Chx) mixtures. The polymers were found to be selective towards Bz. When evaluated against pure Bz and Chx at 27 +/-1 degreesC; PVA-calix showed an ideal selectivity tending towards infinity but a poor flux (5.9 kg mum/(m(2) h)) for Bz. The flux of Bz was significantly higher in PVAc and increased from 20 kg mum/(m(2) h) for 20% (v/v) Bz/Chx mixture to 65.8 kg mum/(m(2) h) for pure Bz. The swelling index also increased with the increasing concentration of Bz in the feed. Pervaporation in PVAc was thus sorption-controlled. The sorption isotherms for the pure components in PVAc were also obtained using an automated sorption analyser based on the principle of mass relaxation of the polymer accompanying vapour sorption. The high interaction of PVAc with Bz was interpreted in terms of solubility parameters and free volume in the polymer. (C) 2003 Elsevier B.V. All rights reserved.