Epoxy resins (DGEBA) were cured by cationic latent thermal catalysts, that is, N-benzylpyrazinium hexafluoroantimonate (BPH) and N-benzylquinoxalinium hexafluoroantimonate (BQH) to investigate the effect of substituted benzene group on cure kinetics and mechanical properties of epoxy system. Differential scanning calorimetry (DSC) was undertaken for activation energy of the system. It was also characterized in terms of flexural, fracture toughness, and Izod impact strengths for the mechanical tests. As a result, the cure reaction of both epoxy systems resulted in an autocatalytic kinetic mechanism accelerated by hydroxyl groups. Also, the conversion and cure activation energy of the DGEBA/BQH system were higher than those of DGEBA/BPH system. The mechanical properties of the DGEBA/BQH system were also superior to those of the DGEBA/BPH system, as well as the morphology. This was probably due to the consequence of the effect of the substituted benzene group of the BQH catalyst, resulting in increasing the crosslinking density and structural stability in the epoxy system studied. (C) 2004 Wiley Periodicals, Inc.