ADDITION OF A REACTIVE DILUENT TO A CATALYZED EPOXY-ANHYDRIDE SYSTEM .1. INFLUENCE ON THE CURE KINETICS

The effect of a reactive diluent (RD) on the kinetics of the curing of an epoxy resin, based on diglycidyl ether of bisphenol A (DGEBA), wit h a carboxylic anhydride derived from methyl-tetrahydrophthalic anhydr ide (MTHPA) catalyzed by a tertiary amine has been studied. The reacti ve diluent was a low-viscosity aliphatic diglycidyl ether, and the com positions per 100 parts by weight (pbw) of DGEBA were 10, 30, and 50 p bw of RD with the stoichiometric quantity of MTHPA and 1 pbw of cataly st. The curing kinetics was monitored by differential scanning calorim etry (DSC), and the kinetic parameters were determined from the noniso thermal DSC curves by the method described by Malek. The kinetic analy sis suggests that the two-parameter autocatalytic model is the more ap propriate to describe the kinetics of the curing reaction of this epox y-anhydride system. The kinetic parameters thus derived satisfactorily simulate both the nonisothermal DSC curves and the isothermal convers ion-time plots. Increasing the RD content leads to a small increase in both the nonisothermal and the isothermal heats of curing and has a s light effect on the kinetic parameters E, In A, m, and n and, conseque ntly, on the overall reactivity of the system. On the other hand, the increase of the RD content significantly affects the structure of the crosslinked epoxy. It is confirmed that the introduction of aliphatic chains in the structure of the epoxy increases the mobility of the seg mental chains in the glass transition region. The consequence of this chemical modification is a decrease of the glass transition temperatur e, T-g. (C) 1996 John Wiley & Sons, Inc.