Kanegafuchi Chemical Ind. Co., Ltd.

Kiyokazu Akahori

Hirosaku Nagano

Hideki Kawai

The present invention provides a copolyimide characterized in that the copolyimide contains units represented by formulas (I) and (II) ##STR1## (wherein R.sub.0 represents an aromatic tetracarboxylic residue). The polyimide has excellent thermal dimensional stability, and can be fabricated by using conventional inexpensive materials.

Polyimide having excellent thermal dimensional stability

Disclosed is a film of polyimide having repeating units of formula (1) and a birefringence (.DELTA.n) of at least 0.13: ##STR1## wherein R.sup.1 is an aromatic group having a valency of 4, at carbon atoms constituting the aromatic ring, and R.sup.2 is an aromatic group having a valency of 2, at carbon atoms constituting the aromatic ring. This polyimide film exhibits good thermal dimensional stability.

Polyimide film

A polyimide copolymer having a repeating unit of formula (I): ##STR1## wherein each of R.sub.1 and R.sub.2 is independently ##STR2## and R.sub.1 and R.sub.2 are different from each other, R.sub.0 is an aromatic group having a valency of 4, and m is a positive integer. The polyimide copolymer is excellent in heat resistance, mechanical properties (e.g., tensile elongation) and thermal dimensional stability.

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Kobe, Japan

Kiyokazu Akahori