In this article, the imidization reaction kinetic of novel poly(ester amic acid)s with azobenzene units as side groups was studied by dynamic experiments by means of differential scanning calorimetry. Polymers differ in the number of chromophore moieties in their repeating unit and position in which azobenzene group is attached to the polymer chain. The kinetic parameters of poly(ester amic acid)s conversion to poly(ester imide)s was compared with data calculated for parent polymer, that is, without azobenzene groups. For the first time to our knowledge, the imidization kinetic of polymers with side azobenzene groups was studied. Kinetic parameters, such as the activation energy and frequency factor were estimated with the by Ozawa model [(E(O) and A(O)), respectively] and Kissinger model RE(K) and A(K), respectively]. The values of activation energy determined with both models were in the range 167.1-198.3 kJ/mol. The lowest activation energy of imidization reaction exhibited polymer in which azobenzene units were placed between amide linkages. Polymers were characterized by FTIR, H-1-NMR, X-ray, and UV-vis methods. The glass transition temperature of resultant poly(ester imide)s was in the range of 217-237 degrees C. The presence of chromophore units slightly decreased T-g and significantly improved their solubility and optical properties. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 118: 2624-2633, 2010