Reactions of DGEBA epoxy cured with diethanolamine: Isoconversional kinetics and implications to network structure

• Published in: Thermochimica acta Vol. 671; no. C; pp. 149 - 160
• Main Authors: McCoy, John D., Ancipink, Windy B., Maestas, Salomon R., Draelos, Lara R., Devries, David B., Kropka, Jamie M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier B.V 01.01.2019; Elsevier
• Subjects: bisphenol A; DGEBA; Diethanolamine; differential scanning calorimetry; epoxides; Epoxy; gelation; hydrogen; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; reaction kinetics; temperature; Tertiary amine; tertiary amines; Tertiary amine; Diethanolamine; Epoxy; DGEBA
• DOI: 10.1016/j.tca.2018.11.013
• ISSN: 0040-6031

[Display omitted] •Tertiary amine activated cure in hydroxyl rich environment.•Primary mechanism is a zwitterion initiated anionic chain-growth polymerization.•Isoconversional times show slowing down and broadening of reaction at high T.•Temperature jumps illustrate cure history dependence of reaction rate.•Proton transfer results in high extent of reaction at gel - unusual for chain-growth. The curing of diglycidyl ether of bisphenol A (DGEBA) epoxy with diethanolamine (DEA) is studied. DEA has three reactive groups, a secondary amine hydrogen and two hydroxyls. The secondary amine reacts rapidly, forming an adduct containing tertiary amines, epoxides and hydroxyls. The epoxides and hydroxyls then react in the presence of the amines to crosslink and vitrify the epoxy in the “gelation” reaction. The gelation reaction, the subject of this study, is not simple. The reaction exhibits unusual dependencies on both temperature and degree of cure. Previously, the general mechanisms of this curing process were explored by a number of us. In the present paper, both differential scanning calorimetry (DSC) and isothermal microcalorimetry (IMC) are used to determine a number of characteristic times associated with the reaction. The characteristic times show that the reaction rate has different functional forms at different temperatures and extents of reaction. This results from the reaction rate not depending solely upon the temperature and over-all extent-of-reaction. The concentration of a number of auxiliary reactive species that are generated in the course of the reaction (as well as their mobility and steric hindrance) appear to be key factors in defining the reaction kinetics. The dependence of the final network structure on cure schedule for this type of tertiary amine activated reaction is then discussed in the context of the literature. Finally, in the Supplementary Material, Kamal-like functions are fit to the isothermal reaction kinetics, with the reader cautioned in applying the functions to non-isothermal cures.