2,3,3',4'-Biphenyltetracarboxylic acid dianhydride

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.

Dependencies are inferred from the claim text.