NCO-terminated polyurethane membranes were prepared using diisocyanate, diol, and trimethylolpropane (IMP) using an NCO/OH ratio of 1.6 : 1. Prepolymer was chain-extended using cellulose acetate butyrate (CAB) in the ratios of 2 :1, 4: 1, and 3: 1 of NCO/OH. Polyurethane (PU) membranes were characterized by differential scanning calorimeter (DSC) and thermogravimetry (TGA) to investigate their thermal properties. Equilibrium sorption studies were carried out at 30 degrees C in water and ethyl acetate media as well as in their binary mixtures. The influence of CAB on pervaporation (PV) separation of an ethyl acetate/water (92/8, w/w, i.e., azeotropic composition) mixture was investigated. Membranes in this study showed a selectivity of 42.42 with a flux value of 0.187 kg/ m/h for 3: 1% NCO/OH containing PU membrane. In order to gain a more detailed picture of the molecular transport phenomenon, we performed the sorption gravimetric experiments at 30 degrees, 35 degrees, 40 degrees, and 50 degrees C to compute diffusion, swelling, sorption, and permeability coefficients of PU membranes in the azeotropic mixture of ethyl acetate and water. Activation parameters for diffusion and permeation were computed from the Arrhenius equation to understand the polymer/solvent interactions. Sorption trends and diffusion anomalies were established through an empirical equation after estimating the diffusion parameters. (c) 2006 Wiley Periodicals, Inc.