Curing kinetics of epoxy resins with hyperbranched polyesters as toughening agents

The effects of hyperbranched polyesters on the cure kinetics of diglycidyl ether of bisphenol A (DGEBA) in the presence of m-phenylene diamine were investigated with nonisothermal differential scanning calorimetry. The results showed that the addition of hyperbranched polyesters enhanced the cure reaction of DGEBA with m-phenylene diamine, and this resulted in a reduction of the peak temperature of the curing curve and the activation energy because of the low viscosity and large number of terminal hydroxyl groups. However, when linear poly(ethylene glycol) was added, the activation energy of the blends also slightly decreased, whereas the peak temperature of the curing curve increased. The curing kinetics of the blends were calculated by the isoconversional method of Malek. The two-parameter autocatalytic model (i.e., the Sestak-Berggren equation) was found to be the most adequate for describing the cure kinetics of the studied systems. The obtained nonisothermal differential scanning calorimetry curves showed results in agreement with those theoretically calculated. (C) 2004 Wiley Periodicals, Inc.