Process for preparing polyimides.
A process for preparing a polyimide by reaction of a diamine and a tetracarboxylic dianhydride to obtain a polyamide acid and subjecting the polyamide acid to conversion into a polyimide thermally or chemically. The reaction in the process is carried out in the presence of at least one dicarboxylic anhydride selected from the group consisting of aliphatic dicarboxylic anhydrides and aromatic dicarboxylic anhydrides, and the amount of the tetracarboxylic dianhydride is in the range of from 0.9 to 1.0 mole per mole of the diamine and the amount of the dicarboxylic anhydride is in the range of from 0.001 to 1.0 mole per mole of the diamine. The resultant polyimides exhibit good thermal stability at high temperatures and good forming processability even at low temperatures.