Patent ID: 7807014

Claim:
A process for preparing a thermosetting solution composition comprising a biphenyltetracarboxylic acid compound containing at least 15 mol % of a partial lower aliphatic alkyl ester of 2,3,3′,4′-biphenyltetracarboxylic acid and/or a partial lower aliphatic alkyl ester of 2,2′,3,3′-biphenyltetracarboxylic acid, an aromatic diamine compound in a molar amount larger than a molar amount of the biphenyltetracarboxylic acid compound, said aromatic diamine compound being selected from the group consisting of p-phenylenediamine, m-phenylenediamine, 1,3-bis(4-aminophenoxy)benzene and a mixture thereof, and a partial lower aliphatic alkyl ester of 4-(2-phenylethynyl)phthalic acid compound in a molar amount as much as 1.8-2.2 times a molar amount corresponding to a difference between the molar amount of the aromatic diamine compound and the molar amount of the biphenyltetracarboxylic acid compound dissolved in an organic solvent comprising a lower aliphatic alcohol, in which a total amount of the biphenyltetracarboxylic acid compound, 4-(2-phenylethynyl)phthalic acid compound and aromatic diamine compound is in the range of 30 to 80 wt. % based on an amount of the thermosetting solution composition, which comprises the steps of: placing a biphenyltetracarboxylic acid compound containing at least 15 molar % of 2,3,3′,4′-biphenyltetracarboxylic dianhydride and/or 2,2′,3,3′-biphenyltetracarboxylic dianhydride, and 4-(2-phenylethynyl)phthalic anhydride in the organic solvent, to give a suspension; heating the suspension to give a solution in which the partial lower aliphatic alkyl ester of the biphenyltetracarboxylic acid compound and the partial lower aliphatic alkyl ester of 4-(2-phenylethynyl)phthalic acid are dissolved; and mixing the aromatic diamine compound with the solution obtained above.