A series of copolyimides (co-PIs) with high molecular weights, excellent mechanical properties, heat-resistant properties, and good solubilities in organic solvents were synthesized from six kinds of commercial dianhydrides (IIa-f) and 1,4-bis(4-aminophenoxy)-2-tert-butylbenzene (I). Monomers (IIa-d) for synthesizing insoluble PIs and monomers (IIe,f) for synthesizing soluble PIs were used to synthesize co-PIs with arbitrary solubilities. Nine kinds of soluble co-PIs (IIIa-e and IVa-d) were synthesized through chemical or thermal cyclodehydration. These co-PIs were found to be easily soluble as well as able to be processed by casting from their solutions such as NMP, DMAc, m-cresol, pyridine, THF, and CH2Cl2. The easily dissolved characteristics of this series of co-PIs stemmed from the t-butyl group and ether group within I. Besides, when the used dianhydride molecules contained the organosoluble groups, the solubilities in organic solvents could be greatly enhanced. The co-PIs could improve the. processability of polymers, while increasing their flexible mechanical properties and maintaining their excellent heat-resistant properties. (C) 2000 John Wiley & Sons, Inc.