Abstract: Highly pure 3,3',4,4'-biphenyltetracarboxylic acid (BPTA) and dianhydride thereof (BPDA) are produced by heating crude BPTA to give BPDA, treating the BPDA with hot water to give highly pure BPTA, and in the case of highly pure BPDA, heat treating the pure BPTA to give highly pure BPDA.
Type:
Grant
Filed:
March 9, 1990
Date of Patent:
September 10, 1991
Assignees:
Hitachi, Ltd., Japan Carlit Co., Ltd., Kanto Koatsu