To effectively suppress the swelling of poly(vinyl alcohol) (PVA) membrane, polymer-inorganic nanocomposite membranes composed of PVA and gamma-mercaptopropyltrimethoxysilane (MPTMS) were prepared by in situ sol-gel technique for pervaporative separation of water-ethylene glycol (EG) mixtures. Effects of the types of catalyst for sol-gel process and MPTMS content on the physical and chemical structure of PVA-silica nanocomposite membranes (designated as PVA-MPTMS hereafter) were investigated by 29 Si NMR, FTIR, SEM, XRD and TGA-DTA. Due to the formation of more compact crosslinked structure, nanocomposite membranes exhibited enhanced thermal stability. It was found that when 50 wt% of MPTMS was incorporated into PVA, the nanocomposite membranes possessed optimum pervaporation performance for 80 wt% EG aqueous solution at 70 degrees C. Unexpectedly, there was no improvement in the pervaporation performance of PVA-MPTMS nanocomposite membranes after mercapto group was oxidized into sulfonic group. (C) 2007 Elsevier Ltd. All rights reserved.