The methylene diisocyanate (MDI) and toluene diisocyanate (TDI) based polyurethane/polybutyl methacrylate (PU/PBMA-50/50) interpenetrating polymer network (IPN) membranes have been prepared. The molecular migration of n-alkane penetrants such as hexane, heptane, octane, nonane, and decane through PU/PBMA (50/50) membranes has been studied at 25, 40, and 60degreesC using a weight gain method. From the sorption results, diffusion (D) and permeation (P) coefficients of n-alkane penetrants have been calculated. Molecular migration depends on membrane-solvent interactions, size of the penetrants, temperature, and availability of free volume within the membrane matrix. Attempts have been made to estimate the parameters of an empirical equation and these data suggest that molecular transport follows Fickian mode. From a study of temperature dependence of transport parameters, activation energy for diffusion (E-D) and permeation (E-P) have been estimated from the Arrhenius relation. Furthermore, sorption results have been interpreted in terms of enthalpy (DeltaH) and entropy (DeltaS) of sorption. The liquid concentration profiles have been computed using Fick's equation with appropriate initial and boundary conditions. (C) 2003 Wiley Periodicals, Inc.