Preparation of 2‐ethyl‐4‐methylimidazole derivatives as latent curing agents and their application in curing epoxy resin

Abstract

Three kinds of 2-ethyl-4-methylimidazole (EMI) derivatives (N-acetyl EMI, N-benzoyl EMI, and N-benzenesulfonyl EMI) were synthesized through the reaction of EMI with acetyl chloride, benzoyl chloride, and benzenesulfonyl chloride, respectively. And the structure was confirmed by Fourier transform infrared spectroscopy (FTIR) and 1 H-nuclear magnetic resonance spectroscopy ( 1 H NMR) spectra. Furthermore, the synthesized EMI derivatives were applied in diglycidyl ether of bisphenol A epoxy resin (DGEBA) as latent curing agent. Differential scanning calorimeter (DSC) was used to analyze the curing behavior of DGEBA/EMI derivative systems, indicating DGEBA could be efficiently cured by the EMI derivatives at 1101608C, and the corresponding curing activation energy ranged from 71 to 86 kJ/mol. Viscosity data proves that the storage life of DGEBA with N-acetyl EMI (NAEMI), N-benzoyl EMI (NBEMI), and N-benzenesulfonyl EMI (NBSEMI) at room temperature was 38 d, 50 d, and 80 d, and that at 108C was 90 d, 115 d, and 170 d, respectively. Besides, thermogravimetry (TG), izod impact strength (IIS), and tensile shear strength (TSS) were tested to characterize the thermal stability and mechanical properties of DGEBA cured by EMI derivatives.

A One-Component, Fast-Cure, and Economical Epoxy Resin System Suitable for Liquid Molding of Automotive Composite Parts

“…Therefore, only a low level is needed to achieve a high T g of the cured epoxy resin, while also maintaining the low cost of the total system. In general, imidazoles have intrinsic high curing reactivity towards epoxy resins, and the curing behaviors can be facilely tailored by introducing various substituent groups on the imidazole rings [ 27 , 28 ]. So far, a large number of imidazole hardeners have been designed and commercialized, providing a generous toolbox to develop one-component and fast-curing epoxy systems [ 29 , 30 , 31 ].…”

Thermal latent curing agent for epoxy resins from neutralization of 2‐methylimidazole with a phosphazene‐containing polyfunctional carboxylic acid

“…Long storage life of the one‐pot epoxy compound is obtained as the blocking of the activity of imidazoles, while rapid curing reaction proceeds at a moderately elevated temperature (100°C‐175°C) after regaining the curing capacity. In addition, no adverse effect should be played on the cured materials . Shin et al encapsulated imidazole derivatives in polycaprolactone microcapsules via either solvent evaporation method or spray‐drying method.…”

Novel imidazole derivatives with recoverable activity as latent curing agents for epoxy

“…Therefore, to extend the storage time of one-component epoxy, latent curing agents, or latent catalysts have been developed. 9,10 Imidazole can be modified to latent curing agents using several methods: microencapsulation technology, [11][12][13][14][15] activity inhibition of secondary amine, [16][17][18][19][20] and activity inhibition of tertiary amine. [21][22][23] The first method involves the production of microcapsules.…”