Patent ID: 8742031

Claim:
A heat-resistant polyimide copolymer soluble in organic polar solvents, consisting of the following four components: biphenyltetracarboxylic dianhydride (BPDA), 4,4′-diaminodiphenyl ether (DADE), pyromellitic dianhydride (PMDA) and 2,4-diaminotoluene (DAT), wherein said heat-resistant polyimide copolymer is a product of a reaction consisting of a first step of producing an oligomer having DADE at both ends of BPDA, then a second step of adding PMDA and DAT to form an imide oligomer having PMDA at both ends, and a third step of adding DAT to polycondense the mixture, and wherein said heat-resistant polyimide copoloymer has a glass transition temperature of 430° C. or more.