The combination of the electrical conducting properties of polyaniline (Pani) with the mechanical performance of polyurethanes (PU) was accomplished through the interconnection of the two polymers via condensation of a NCO terminated PU prepolymer and the amine groups of polyaniline. The crosslinking density of the resulting networks was set by the proportion between the two components, since the PU length was kept constant (M-w = 40, 000, M-n = 23, 000). The composition range Pani/PU spanned from 1 to 30%. Blends of the same composition were prepared for comparison purposes. Taking into account the IR absorption shifts, DMTA spectra, electrical conductivity results and computer generated optimized chain conformation, a morphological interpretation is proposed in which Pani chains form a continuous percolating phase dispersed in a polyurethane matrix, linked together by an interphase, with a certain degree of miscibility. This interphase would be responsible for the connectivity between the two components and the good mechanical properties observed. Electrical conductivity of the networks was in the 10(-4) S/cm range. (C) 2003 Elsevier Ltd. All rights reserved.