Cure kinetics of diglycidylether of bisphenol A– ethylenediamine revisited using a mechanistic model

Abstract

ABSTRACT:The polymerization kinetics of the reaction between diglycidylether of bisphenol A (DGEBA) and ethylenediamine (EDA) was analyzed, using dynamic scanning calorimetry, in both isothermal and programmed heating-rate modes. A simple mechanistic model, consisting of an equilibrium reaction generating an epoxy-hydroxyl complex, and including two possible mechanisms for the consumption of amine hydrogens [(1) with free epoxy groups, (2) with the epoxy-hydroxyl complex], provided a reasonable fitting of the whole set of experimental results. It was found that the equilibrium constant decreased with temperature, making less important the reaction mechanism involving the epoxy-hydroxyl complex.

Modeling the Cure of an Epoxy‐Amine Resin with Bisphenol A as an External Catalyst

“…Figure 8 shows the concentration of the two epoxyhydroxyl complexes as a function of conversion. The curves related to E-OH 2 show the same trend as those reported by Riccardi et al [17] with DGEBA-EDA. All the curves go through a maximum which can be explained by the competition between the rise in the concentration of hydroxyl and the decrease in the concentration of total epoxy groups, on increasing conversion.…”

“…As expected, the differences between pseudo and true k 2 decrease on increasing temperature which is a direct consequence of the decrease of equilibrium constant K 2 on increasing temperature. This effect is more pronounced for DGEBA-EDA compared with the present system owing to the lower equilibrium constant values reported by Riccardi et al [17] for the former. The k 2 values of the present epoxy-amine system are in excellent agreement with those of the DGEBA-Jeffamine D400 given by Siddiqi et al [24] Despite its complexity, the global reactivity of the present system is well described by the reactivity of its main amine component (93.4 wt.-%), namely Jeffamine D230.…”

“…From a mechanistic approach, few authors have extended the Horie treatment to include these side reactions. [13][14][15][16] To improve the fundamental knowledge of epoxy-amine cure, mechanistic reaction models were developed based on the existence of different termolecular and tetramolecular transition complexes [2,3,[17][18][19] whose formation has been shown [18] or supposed [3] to be the rate determining step. The first step includes the formation of bimolecular donor-acceptor complexes (Scheme 1).…”

“…[3,19] So far, the validity of the different paths shown in Scheme 1 has been discussed based on experimental data obtained with model compounds [3,18,19] or with simple and pure DGEBA-amine systems. [17,19] The aim of this paper is to characterize and study the cure mechanism of a complex commercial epoxy-amine system. The specificity of the epoxy-amine system is the presence of a low amount of bisphenol A (BPA) added as an external catalyst in the hardener.…”

“…Figure 11 shows the change of k 2 with temperature determined from the two above mentioned methods. Data from DGEBA-ethylenediamine [12,17] and DGEBAJeffamineD400 [24] have also been inserted for comparison with the present epoxy-amine system. The pseudo k 2 values extracted from the (da/dt)/(1 À a) 2 versus a plots are found to differ from the true k 2 values ('true' in the sense that they are determined through the kinetic equations derived from the pre-equilibrium mechanism).…”