Method for producing bisimide dicarboxylic acid

A method for producing a bisimide dicarboxylic acid with a tricarboxylic acid anhydride and a diamine, where said tricarboxylic acid anhydride is an aromatic tricarboxylic acid anhydride, an alicyclic tricarboxylic acid anhydride, or a mixture thereof and wherein said diamine is an aliphatic diamine, an alicyclic diamine, an aromatic diamine, or a mixture thereof, the method comprising the following processes (i) and (ii):

• a process (i) in which, provided that a compound having a higher melting point is a high melting compound and a compound having a lower melting point is a low melting compound, when a melting point is compared between the tricarboxylic acid anhydride and the diamine, the high melting compound is heated at a temperature between less than the melting point of the high melting compound and not lower than the melting point of the low melting compound, and the low melting compound is added, in a melted state, at a temperature in a range lower by 5 to 10° C. or more than the ng point of the high melting compound and at a temperature in a range higher by 5 to 10° C. or more than the melting point of the low melting compound and at an addition rate from 0.005 to 2.00% by mass/minute to the high melting compound, while the high melting compound maintains its solid state, to give a mixture;
• and
• a process (ii) in which the resultant mixture in the process (i) is heated while the solid state of the high melting compound is kept, and the melted state of the low melting compound is kept;
• to give bisimide dicarboxylic acid.