Chemically oxidative polymerization of o-phenylenediamine and 2,3-xylidine (XY) with three molar ratios was performed by using ammonium persulfate as an oxidant in boiling glacial acetic acid. The polymerization yield decreases significantly but the intrinsic viscosity of the polymers remains almost constant with increasing feed content of XY monomer. The resulting polymers were characterized by H-1-nuclear magnetic resonance. UV-vis and Fourier transform infrared spectroscopies, wide-angle X-ray diffraction, and thermogravimetry methods. The results showed that the polymers are amorphous and exhibit a thermal decomposition temperature higher than 500 degreesC. the maximum weight-loss rate lower than 5%/min in nitrogen and air. Char yield at 700 degreesC for the polymers is larger than 32 wt% in nitrogen but nearly zero in air. The activation energy, order, and frequency factor of thermal decomposition for the copolymers were 43-53 kJ/mol. 0.4-1.3, and 13.5-181.3 min(-1) in nitrogen and air. (C) 2001 Elsevier Science Ltd. All rights reserved.