The free-radical copolymerization of methyl methacrylate (MMA) with N-P-tolylmalemide (NPTMI) at 77degreesC in cyclohexanone solution initiated by AIBN was studied. The copolymer composition was calculated from the nitrogen content estimated by the Mico-Kijedldahl's method and by elemental analysis. The reactivity ratios have been calculated by Fineman and Ross method. The monomer reactivity ratios were r(NPTMI) 1.24, r(MMA) = 2.1. The glass transition temperature (T-g) of the copolymers were determined by torsion braid analysis (TBA). The thermal stability was determined by thermogravimetric analysis (TGA). T-50, temperature at which the weight loss reaches 50%, was abstained. The results showed that the (M) over bar (n) and (M) over bar (w). increased, whereas the NPTMI feed content increased. The T-g and T-50 increased dramatically. (C) 2003 Wiley Periodicals, Inc.