The kinetics and mechanisms of the solution imidization of polyamic acid resulting from a diamine, bis(4-aminophenoxy-3,5-dimethylphenyl)naphthylmethane, and a dianhydride, 3,3'4,4'-diphenylsulfonetetracarboxylic dianhydride, were studied at three various temperatures (145, 165, and 180 degreesC). The results were confirmed by means of H-1 NMR and gel permeation chromatography (GPC). Kinetic parameters were obtained by an isothermal study, and the results were quite close to second-order kinetics for the homogeneous solution imidization. In addition, Carother's equation, Mark-Houwink theory, and GPC were used to explain the molecular weight of the imidization processes. The apparent activation energy (E-a) was 104 KJ/mol, and the pre-exponential factor (k(0)) was 3.48 x 10(14). The proposed kinetic mechanism is in good agreement with the kinetic models.