EFFECT OF STOICHIOMETRY AND DIFFUSION ON AN EPOXY-AMINE REACTION-MECHANISM

The bulk phase kinetics of an epoxy (DGEBA)/amine (DDS) thermoset have been studied using DSC, FTIR, and C-13-NMR. In the absence of catalys t, the reaction was found to involve a main exothermic reaction betwee n epoxide and amine hydrogen and a side reaction between tertiary amin e formed in the main reaction and epoxide. The main reaction was exoth ermic while the side reaction had no discernable exotherm. Etherificat ion did not occur to any significant extent. Since only the main react ion is exothermic, DSC was very useful for studying the main reaction kinetics. FTIR was used for determining whether epoxide and amine hydr ogen were consumed at different rates as a way of following the side r eaction. An IR band previously unused by other investigators was used to monitor the amine hydrogen concentration. NMR confirmed the above m echanism by identifying the formation of a quaternary ammonium ion/alk oxide ion pair as a reaction product of tertiary amine and epoxide. Th is mechanism has been successfully fit to a rate law valid over the en tire extent of reaction. The rate constant for the epoxy/amine additio n reaction was found to depend on hydroxide concentration (extent), re action temperature, and glass transition temperature and included cont ributions from uncatalyzed and autocatalyzed parts. The side reaction (quaternary ammonium ion formation) formed weak bonds which did not af fect the overall system T-g. Both reactions were second order. The rat e constants for the main reaction first increase with increasing exten t due to autocatalysis by hydroxide before decreasing due to the diffu sion limit caused by gelation and vitrification. (C) 1995 John Wiley & Sons, Inc.