A series of aromatic copolyimides was successfully synthesized from the commercial pyromellitic dianhydride(PMDA)with the commercial diamine P-phenyldiamine(PDA)and the diamine 4

4’-methylenebis-(2-tert-butylaniline)(MBTBA)specially designed by ourselves．The copolyimides were characterized by IR

NMR

GPC．UV-Vis．TGA and DMA．The copolyimide was precipitated in m—cresol in the polymerization process when the molar ratio of MBTBA and PDA was lower than 6／4．The number-average molecular weight of the soluble copolyimides measured by GPC was larger than 4．0×104 and the polydispersity index was higher than 1．5．Only one glass transition temperature of these copolyimdies was detected around 360℃ by DMA．The copolyimides did not show appreciable decomposition up to 500℃ under N2

and the thermal stability of the conyimide increased a little with the intreduction of the PDA into the polymer chains．