Hydroxyterminated-polybutadiene-based prepolyurethanes were prepared with two different catalysts, dibutyltindilaurate (DBTDL) and triethylamine (TEA); chain extension of the prepolyurethanes followed with two different aromatic diamines, oxydianiline and 4,4 ' -diaminodiphenylsulfone, in various concentrations. The prepolyurethane synthesis followed second-order kinetics, with the DBTDL catalyst showing better efficiency for urethane formation than TEA. TEA-catalyzed synthesis suffered from the self-association of isocyanates as a major side reaction, following second-order kinetics with respect to isocyanate concentration. Although there was a gradual increase in the intrinsic viscosity during prepolyurethane synthesis in the presence of DBTDL, the intrinsic viscosity remained almost constant with the progress of the reaction in the presence of TEA. The tensile properties of prepolyurethane and polyurethaneureas synthesized in DBTDL-catalyzed reactions were higher than the properties of those synthesized in TEA-catalyzed reactions. The variation of the tensile strength with the diamine concentration was correlated with the crosslink density and Sol fraction. The solubility of the hard segment of polyurethaneurea in the reaction medium appeared to be important in influencing the tensile properties. The effects of the diamine concentration (chain extender) on the diffusion coefficient and activation energy of diffusion of toluene in polyurethaneureas were studied.