Membranes of hydroxyl terminated polybutadiene (HTPB) and 4,4’-dicyclohexylmethane diisocyanate (H(12)MDI) based polyurethane (PU) crosslinked with benzoyl peroxide (BPO) and then formed into an interpenetrating network (IPN) with 4-vinyl pyridine (4-VP) were utilized for the pervaporation separation of water-ethanol mixtures. Membranes of IPN with a content of 8.44 wt% 4-VP have a permeability of 1184 g/m(2) h and a separation factor of 4.11 at 90 wt% aqueous ethanol solution. The effect of hydrophilic-hydrophobic content variation and the crosslinking on the adsorption, transport and morphological properties were investigated. The hydrogen bonding index (HBI) and frequency difference as a measure of the phase segregation and the average strength of the interpolymer hydrogen bonds were utilized to study the sorption phenomenon and permselectivity of the prepared membranes. The change of the glass transition temperature and infrared spectra, which can be used to show the 4-VP content, were detected by DSC and FTIR, respectively. Thermal decomposition behaviors conducted by TGA were used to investigate the formation of IPN.