New investigation of 1‐substituted imidazole derivatives as thermal latent catalysts for epoxy‐phenolic resins

Abstract

Novel 1-substituted imidazole derivatives (4-10) were synthesized by imidazole and the corresponding substituted reagents (chloromethylpivalate, diphenylphosphinicchloride, di-tert-butyldicarbonate, 1,1 0 -oxalylchloride, pyrazine, phneylisocyanat, and p-toluensulfonylchloride). Polymerization of diglycidyl ether of bisphenol A (DGEBA) with 1-substituted imidazole derivatives, two commercial available catalysts (imidazole and 1-cyanoethyl-2-ethyl-4methylimidazole) and N-benzylpyrazinium hexafluoroantimonate were investigated as model reactions of epoxy resin systems with respect to the thermal latency and storage stability of the catalysts. The catalytic activity of 1-substituted imidazole derivatives 4-10 depended on the steric and withdrawing electronic effect of the substitution groups. To characterize the cure activation energy and the viscosity-storage time, the order of thermally latent activity is 1-tosylimidazole (6) > 1,1 0

Improvement of the thermal latency for epoxy-phenolic resins by novel amphiphatic imidazole catalysts

“…31 For DGEBA cured with imidazole 1-3, the T g value indicated the complete or near complete curing systems in the temperature range of 151-159 o C. The results were consistent with the published data. 19,30 When weak acidic catalysts 4 and 5 were applied in cur- ing DGEBA, the T g value could not be detected between 30-300 o C at the heating rate of 10 o C/min. Application of the same conditions for the cure of DGEBA by amphiphatic catalysts 6-9, the T g values could be obtained, which ranged from 152 to 163 o C (see Table IV and Figure 5).…”

“…The approaches involve the preparation of metal Lewis acid-imidazole complex (e.g. metals acetylacetone-imidazole complex), 17 the formation of 1,3-disubstituted imidazolium salts 18 and 1-substituted imidazole derivatives, 19 and the modification by blending with the organic carboxylic acids (e.g. benzoic acid, isophthalic acid, and trimellitate).…”

Investigation of soluble PEG-imidazoles as the thermal latency catalysts for epoxy-phenolic resins

“…hardener, and filter) [36]. For DGEBA cured with imidazole and 2E4M-CN, the T g value indicated the complete or near complete curing systems in 151°C and 150°C, respectively [17]. When soluble PEG-imidazole catalysts 1-4 were applied in curing DGEBA, the T g value could be obtained, which ranged from 156°C to 159°C (see Table 3 and Fig.…”

“…Many approaches have been carried out on reducing the activity of imidazoles, including the preparation of metal Lewis acid-imidazole complex (e.g. metals acetylacetone-imidazole complex) [15,16], the formation of 1,3-disubstituted imidazolium salts and 1-substituted imidazole derivatives [17], and the modification by blending with the intermolecular acids (e.g. benzoic acid, isophthalic acid, and trimellitate) [18] or intramolecular acidic groups (carboxylic or amino acid groups) [19].…”

Amphiphatic Piperazine, Pyrazine, and Pyridine Derivaties as the Thermal Latency for Epoxy-Phenolic Resins

“…As a result, latent catalysts were developed to improve the pot life at room temperature for biphenyl type epoxy resins. [7][8][9][10] Latent catalysts in an epoxy resin system can be classified into two groups: thermal 10 and cationic latent catalyst. 9 Most of cationic latent catalysts including piperazine, 11 pyrazine, [12][13][14][15] and pyridine [16][17][18][19] as the core were published in recent year, in which the reactivity of cationic latent catalysts were enhanced by the nucleophilicity of the couterion (BF 4 À , PF 6 À , AsF 6 À and SbF 6 À ).…”