The thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (DGEBA n = 0)/1,2-diamine cyclohexane (DCH) containing different concentrations of an epoxy reactive diluent, vinylcyclohexene dioxide (VCHD), was studied by thermogravimetric analysis to determine the reaction mechanism of the degradation process for these two systems. Values of the activation energy, necessary for this study, were calculated by using various integral and differential methods. Values obtained by using the different methods were compared to the value obtained by Kissinger's method, which does not require a knowledge of the reaction mechanism. All the experimental results were compared to master curves in the range of Doyle's approximation (20-35% of conversion). Analysis of the results suggests that the two reaction mechanisms are R-n and F-n deceleratory type in contrast with the sigmoidal A(2) type of the system with filler and the sigmoidal A(4) type of the system without additives. (C) 2004 Wiley Periodicals, Inc.