Novel copolyimides containing crown ether groups in the diamine moieties were synthesized from 3,3',4,4'-diphenylsulphone tetracarboxylic dianhydride (DSDA), trans-4,4'-diaminodibenzo-18-crown-6 (DABC) and 2,8(6)-dimethyl-3,7-diaminobenzothiophene-5,5-dioxane (DDBT), and their pervaporation properties to benzene/cyclohexane mixtures were investigated. The incorporation of DABC units into DSDA-DDBT resulted in the denser packing of polymer chains. DSDA-DABC/DDBT (1/9 in molar ratio) membrane displayed reasonably high permeation fluxes and high separation factors, that is, a specific permeation flux of 1.6 kg mum/m(2) h and a separation factor of 28 for a mixture of benzene/cyclohexane (60/40 in wt.%) at 343 K. Slight incorporation (10 mol%) of DABC units enhanced the PV performance to some extent, but further incorporation significantly spoiled it. (C) 2004 Elsevier B.V. All rights reserved.