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 glycidyl ether with 2-ethyl-4-methylimidazole (PGE-EMI), has been prepared with the acetato and chloro transition metal salts of Mn, Co, Ni, Cu, Zn, and Ag. These complexes have been characterized using spectroscopic methods (IR, UV-Vis, 1H- and 13C-NMR, where appropriate) and their thermal stabilities have been determined using elevated temperature NMR techniques. These high-temperature NMR results indicated that the chloro complexes studied (of Mn2+, Co2+, Ni2+, Cu2+, and Zn2+) exist in equilibrium (i.e., they dissociate reversibly in a solution of dimethylsulphoxide, DMSO, at elevated temperatures), while the corresponding acetato complexes dissociate irreversibly. For the silver complexes, thermogravimetric analysis (TGA) was used to monitor the dissociation, showing that the weight loss recorded was consistent with the dissociation of the metal salt to liberate the PGE–imidazole ligand. The thermal stabilities of the metal complexes were influenced by changing both the transition metal (e.g., from Mn to Zn) and varying the anion (e.g., from acetate to chloride). From 1H-NMR analysis, a decrease of ca. 10°C was observed in the thermal dissociation of the acetato complexes when compared with the chloro complexes, showing that the series of PGE-EMI complexes with acetate anions is less thermally stable than the corresponding chlorides. This finding suggests that these PGE-EMI complexes may be modified to accommodate their use in a variety of different curing schedules when used to cure epoxy resins. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 201–217, 2000