Preparation, characterization, and thermal properties of controllable metal-imidazole complex curing agents for epoxy resins

A series of complexes incorporating the epoxy-imidazole adduct of phenyl gl ycidyl ether with 2-ethyl-4-methylimidazole (PGE-EMI), has been prepared wi th the acetato and chloro transition metal salts of Mn, Co, Ni, Cu, Zn, and Ag. These complexes have been characterized using spectroscopic methods (I R, UV-Vis, H-1- and C-13-NMR, where appropriate) and their thermal stabilit ies have been determined using elevated temperature NMR techniques. These h igh-temperature NMR results indicated that the chloro complexes studied (of Mn2+, Co2+, Ni2+, Cu2+ and Zn2+) exist in equilibrium (i.e., they dissocia te reversibly in a solution of dimethylsulphoxide, DMSO, at elevated temper atures), while the corresponding acetato complexes dissociate irreversibly. For the silver complexes, thermogravimetric analysis (TGA) was used to mon itor the dissociation, showing that the weight loss recorded was consistent with the dissociation of the metal salt to liberate the PGE-imidazole Liga nd. The thermal stabilities of the metal complexes were influenced by chang ing both the transition metal (e.g., from Mn to Zn) and varying the anion ( e.g., from acetate to chloride). From IH-NMR analysis, a decrease of ca. 10 degrees C was observed in the thermal dissociation of the acetato complexe s when compared with the chloro complexes, showing that the series of PGE-E MI complexes with acetate anions is less thermally stable than the correspo nding chlorides. This finding suggests that these PGE-EMI complexes may be modified to accommodate their use in a variety of different curing schedule s when used to cure epoxy resins. (C) 2000 John Wiley & Sons, Inc.