Theoretical Study on Mechanisms of the Epoxy−Amine Curing Reaction

Abstract

Fundamental understanding of mechanisms of the epoxy-amine curing reaction is crucial for developing new polymer materials. Nearly all experimental studies, to date for elucidating its mechanisms are based on thermometric measurements and thus cannot provide the molecular level details. This study used density functional theory (DFT) methods to examine the mechanism of epoxy-amine poly addition reactions at the molecular level. Different reaction pathways involving both acyclic and cyclic transition state structures were examined for different reaction conditions, namely isolated, self-promoted by amine, catalyzed by alcohol, and in different solvents. The results indicate that the reactions catalyzed by an alcohol dominate the rate over the self-promoted reaction by other amine species and the isolated one in early stages of the conversion. The concerted pathways involving cyclic transition-state complexes are not significant due to their high activation energies. Calculated activation energies are within the experimental uncertainty. In addition, solvent, not steric and electronic effects as suggested earlier, are shown to be responsible for secondary amines to react slower than primary amines.

Structural analysis of the curing of epoxy thermosets crosslinked with hyperbranched poly(ethyleneimine)s

“…The real mechanism can be significantly more complex, involving the formation a number of reaction complexes [50][51][52][53], but this may have limited influence on the structure development during curing.…”

A qualitative, process-parameter-based model for the release agent transfer during CFRP-part production: an approach to increase the initial bondability

“…Within typical epoxy systems the epoxy resin react within a polyaddition with an amine hardener [28]. Unfortunately, the amine hardeners are hygroscopic and have the tendency to react within side reactions with water [29], for example shown by Sanjana et al [30] for the reactivity of an epoxy based prepreg.…”

Infrared Spectroscopy - Materials Science, Engineering and Technology

“…The autocatalysis is attributed to the formation of complex between generated or initially present hydroxyl groups, amino groups and epoxy groups. A simple reaction mechanism is presented in Figure 3 although it can be improved considering some equilibrium reactions for the complexes formation (Ehlers et al, 2007). With appropriate mass balances it is possible to set out rate equations that can be fitted to experimental data to extract the relevant kinetic parameters…”