Octa(maleimido phenyl) silsesquioxane (OMPS) was prepared from octa(aminophenyl) silsesquioxane (OAPS) and maleic anhydride. Initially, octaphenyl silsesquioxane was prepared, and it was nitrated to obtain octa(nitrophenyl) silsesquioxane; subsequently, reduction was carried out to obtain OAPS. These compounds were characterized with Fourier transform infrared, NMR, gel permeation chromatography, and wide-angle X-ray diffraction. Differential scanning calorimetry scans of OMPS showed an exotherm above 100 degrees C, and it was attributed to the curing. The peak maximum temperature depended on the heating rate. Both Ozawa's and Kissinger's methods were used to determine the activation energy for the curing reaction, which was approximately 29 kcal/mol. OMPS was copolymerized with various molar percentages of (1) N,N '-p-phenylenedimaleimide (PPMI) and (2) urethane methacrylate (UMA) by thermal and free-radical polymerization, respectively. The copolymers were characterized with differential scanning calorimetry, dielectric analysis, thermogravimetric analysis, and wide-angle X-ray diffraction. In the PPMI and UMA copolymer series, the glass-transition temperature increased with an increase in the OMPS concentration. The permittivity of the UMA copolymers decreased and tan 6 increased with an increase in the OMPS concentration. In air and nitrogen atmospheres, the thermal stability of the PPMI and UMA copolymers increased with an increase in the OMPS concentration. (c) 2005 Wiley Periodicals, Inc.