A new kind of aromatic unsymmetrical diamine monomer containing thiazole ring, 2-amino-5-(4-aminophenyl)-thiazole (AAPT), was synthesized. A series of novel polyimides were prepared by polycondensation of AAPT with various aromatic dianhydrides by one-step polyimidation process. The synthesized polyimides had inherent viscosity values of 0.36-0.69 dL/g and were easily dissolved in highly dipolar solvents. Meanwhile, strong and flexible polyimide films were obtained, which have good thermal and thermo-oxidative stability with the glass transition temperatures (T-g) of 276.7-346.1 degrees C, the temperature at 5% weight loss of 451-492 degrees C in nitrogen and 422-440 degrees C in air, as well as have outstanding mechanical properties with the tensile strengths of 94-122 MPa, elongations at breakage of 5-18%. These films also had dielectric constants of 3.12-3.38 at 10 MHz. (c) 2007 Wiley Periodicals, Inc.