Imidization of polyamic acid prepared from pyromellitic dianhydride and 4,4'-methylenedianiline was investigated at 373-493 K. A t a certain degree of imidization, depending on the reaction temperature, the reaction is significantly slowed down. For this reason, imidization was divided into two phases, a fast and a slow one, and the rate constants were calculated from the kinetic equation of a first-order reaction. At imidization temperature above 443 K the activation enthalpy of the reaction decreases, probably due to the thermal decomposition of complexes of o-carboxybenzamide groups with residues of the solvent. At higher imidization temperatures also the activation entropy of imidization decreases; this is probably caused by the higher rigidity of the film because of evaporation of the solvent which acts as a plasticizer.
Ar, Ar': aromatic structuresUsually, technological applications call for an increase in temperature from ca. 373 K to 573 K4). Only at high temperatures (>573 K) a complete transformation of ocarboxybenzamide groups into benzimide structures can be achieved. A very high degree of imidization is important predominantly in microelectronic applications, 0 1990, Hiithig & Wepf Verlag, Base1CCC 0025-1 16X/90/$03.00