The copoly(amic acid)s were prepared from two various diamines 2,2'-bis (4-aminophenoxy phenyl) hexafluoropropane or 2,2'-bis (4-aminophenoxy phenyl) propane and amine-terminated oligosiloxane, respectively, with aromatic tetracarboxylic dianhydride (3,3',4,4'-benzophenone tetracarboxylic dianhydride). The resulted copoly(amic acid) with various mole ratio of triallyl isocyanurate (TAIC)/4,4'-bismaleimidopheny1methane (BMI) were subsequently thermally imidized to the corresponding copolyimides. These polymers were characterized using viscometer, differential scanning calorimetry, thermogravimetric analyses, dynamic mechanical analysis (DMA), dielectric analyzer, and scanning electron microscope. The dielectric constant (D-K) and dissipation factor (D-f) of copolyimides with TAIC/BMI were much lower than that of copolyimides without TAIC/BMI. Furthermore, the formation of copolyimides also would enhance their thermal stability and solubility. DMA of copolymers showed only a glass transition temperature (T-g), indicating a random structure and an amorphous state. The morphology of copolyimides revealed no phase separation. This indicates that the homogeneous state has been achieved in this coreaction system. (c) 2007 Wiley Periodicals, Inc.