In the present work, a series of aromatic/aliphatic co-polyureas have been synthesized from 4,4-diphenylmethane diisocyanate (MDI), in-phenylene diamine (m-PDA), and 1,6-diaminohexane (HDA) in DMAc by a two-stage solution polymerization route. Characterizations of the polyurea products have been carried out by H-1-nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopic techniques. Thermal properties of the polyurea samples have been investigated by differential scanning calorimetry and thermogravimetric analysis. The mechanical properties of the polyurea samples have been measured. The results show that the polyurea samples with the expected structure have been synthesized. The results of DSC analysis show the glass transition temperatures of the co-polyurea samples decrease with the increase of HDA content, and fit the Fox equation well. TGA data of the polyurea samples indicate that thermal stability of the aromatic polyurea is better than that of the co-polyureas. The thermal degradation activation energies of the co-polyureas are similar to 60-70 kJ/mol. The results of mechanical measurement show that the initial modulus and tensile strength of the co-polyurea samples decrease with the increase of HDA content. (C) 2008 Wiley Periodicals, Inc.