Castor oil based chain extended polyurethanes (PUs) have been prepared using citric acid and maleic acid as chain extenders. Molecular transport of n-alkanes into prepared carboxylic acid chain extended PUs has been studied at different temperatures, viz., 25, 40, and 60 degrees C using a gravimetric sorption method. The sorption (S), the diffusion (D), and the permeation (P) coefficients for n-alkane penetrants have been calculated. Transport data are affected by the nature of the interacting solvent molecules, molar volume, solubility parameters, temperature, and the structural variation of the chain extended PUs. The temperature dependence of the transport coefficient has been used to estimate the kinetic parameters for the processes of diffusion (E-D) and permeation (E-P) from the Arrhenius plots. The van't Hoff relation was used to obtain enthalpy (Delta H) and entropy (Delta S) of sorption process. POLYM. ENG. SCI., 47:2057-2064, 2007. (C) 2007 Society of Plastics Engineers.