Thermally stable copolyimides were prepared from two novel second-order nonlinear optical chromophores containing diamines, 4-nitro-4＇-[N-(4,6-di-beta-aminoethylamino)- 1,3,5-triazin-2-yl] aminoazobenzene (M1) and 4-nitro-4＇- [N-(4,6-di-4-aminophenylamino)-1,3,5-triazin-2-yl] aminoazobenzene (M2); two codiamines, 4,4＇-diamino-3,3＇-dimethyl diphenylmethane (MMDA) and bis-(3-aminopropyl)-1,1＇,3,3＇-tetramethyldisiloxane (SiDA); and 3,3＇,4,4＇-diphenyl ether tetracarboxylic acid dianhydride (OPDA). All copolyimides possess high glass transition temperatures (T-g＇s) between 237 and 271 degrees C. Copolyimides based on M2 do not exhibit an obvious change in T-g as the M2 content is increased, while those based on M1 show a slight decrease in T-g as the M1 content is increased. All copolyimides exhibit high thermal decomposition temperatures. The copolyimides are soluble in aprotic solvents such as NMP, DMAc, DMF, DMSO, and 1,4-butyrolactone. Some are even soluble in common low boiling point solvents such as THF and chloroform. The refractive index of a copolyimide is increased as the chromophore content is increased, while the birefringence of a copolyimide does not exhibit strong dependence on the chromophore content. (C) 2000 John Wiley & Sons, Inc.