The application of the "pore-filling" concept yielded aromatic hydrocarbon selective composite membranes. Asymmetric poly(acrylonitrile) ultrafiltration membranes with an average pore size of about 9 urn were used as support for the development of pervaporation separation phases prepared in situ by heterogeneous photo-initiated graft copolymerization in water. The impact of different substituted methacrylates, acrylates or vinylates, preparation and membrane parameters (UV irradiation time and degree of grafting) were analyzed using pervaporation with toluene/n-heptane mixtures (20/80 wt.-ratio; 80degreesC) as feed. In the same way multi-component aromatic/aliphatic mixtures were studied. High aromatic hydrocarbon selectivity and good permeate flux were achieved. Major reasons for the excellent performance of the membranes were the small effective barrier thickness (<3 mum) and the suppressed swelling of the graft copolymer caused by the covalent anchoring in the pore structure. (C) 2004 Elsevier B.V. All rights reserved.