| abstract |
PURPOSE:To produce the title film in improved industrial continuous productivity by casting a specified polyamic acid solution on a substrate, heating the cast solution, releasing the obtained self-supporting film from the substrate and further heating the film. CONSTITUTION:3,4,3',4'-biphenyltetracarboxylic dianhydride is polymerized with a substantially equimolar amount of p-phenylenediamine at 0-80 deg.C in an organic polar solvent to obtain a polyamic acid (A). An organic polar solvent other than a nitrogeneous heterocyclic compound having a resonance structure is mixed with 0.02-0.4 equivalent, per equivalent of the amic acid units of component A, of isoquinoline or a substituted pyridine to obtain a mixed solvent (B) substantially free from lower carboxylic acid anhydrides. Component A is dissolved in component B to obtain a polyamic acid solution. This solution is cast on a substrate and heated to 80-200 deg.C to obtain a self-supporting film. This film is released from the substrate and further heated to 300 deg.C or above to obtain the title film. |