Isothermal melt crystallization kinetics and nonisothermal cold crystallization kinetics of co-PI based on 3, 3', 4, 4'-biphenyltetracarboxylic dianhydride (s-BPDA)/1, 3-bis-(4-aminophenoxy) benzene (TPER)/4, 4'-oxydianiline(4, 4'-ODA), and TPER PI (s-BPDA/TPER) have been investigated. Avrami equation was used to analyze isothermal melt crystallization progress of TPER PI and co-PI, primary crystallization processes was found to be changed as the introduction of 4, 4'-ODA. Total activation energy ?E for TPER PI and co-PI were found to be -404 and -86 kJ mol-1 by Arrhenius equation. Jeziorny's analysis, Ozawa's analysis, and Mo's approach were used to investigate nonisothermal cold crystallization progress of TPER PI and co-PI. Activation energy ?Enon for TPER PI and co-PI were found to be 247 and 193 kJ mol-1 by Kissinger equation. The result indicated that co-PI exhibited lower crystallization rate than TPER PI when isothermally crystallized from melt, but higher crystallization rate under cold nonisothermal crystallization progress. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013