Process for the preparation of aromatic polyimide film

A process for the preparation of an aromatic polyimide film comprising the steps of:

• casting a polyamide acid solution on a support in the form of a film, said polyamide acid solution comprising a polyamide acid obtained by the polymerization reaction of 3,4,3',4'-biphenyltetracarboxylic dianhydride and p-phenylenediamine in a polar organic solvent other than a nitrogen atom-containing heterocyclic compound having a resonance structure in the presence of an imidization agent selected from the group consisting of isoquinoline and a substituted pyridine, said imidization agent being used in an amount of 0.02 to 0.4 gram equivalent per 1 gram equivalent of an amide acid unit of the poly-amide acid and in the absence of a lower fatty acid anhydride;
• heating the cast solution on the support at a temperature of 80.degree. to 200.degree. C. to obtain a self-supportable film;
• peeling the self-supportable film from the support;
• and
• heating the film at a temperature of not lower than 300.degree. C.