The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Sep. 13, 1977
Filed:
Jul. 21, 1975
Hiroshi Itatani, Ichihara, JA;
Mikito Kashima, Ichihara, JA;
Masaoki Matsuda, Ichihara, JA;
Hataaki Yoshimoto, Ichihara, JA;
Hiroyuki Yamamoto, Ichihara, JA;
UBE Industries, Ltd., Ube, JA;
Abstract
A process for separating and purifying biphenyltetracarboxylic dianhydride isomers from a mixture of these isomers by fractional crystallization in aliphatic acid anhydrides or acetone. The isomeric mixture is obtained by heating biphenyltetracarboxylic acids, optionally in the presence of an aliphatic acid anhydride. The biphenyltetracarboxylic acids are obtained by oxidizing coupling dimers of o-xylene or by hydrolyzing coupling dimers of dimethyl phthalate. 2,3,3',4'-biphenyltetracarboxylic acid dianhydride which can be isolated from the above mixture can be used to form polyimide.