2-Phenylimidazole (2-PI) is used to prepare complex compounds with ruthenium (III) and also as an intermediate for agrochemical, pharmaceutical and specialty products. It also finds its application as a curing agent for epoxy resins and polyurethane [1].

Study of Mechanism of Epoxide by Imidazole

In 1987, Jíšová, Václava studied the curing mechanism of epoxide by imidazole. Some imidazoles are highly effective curing agents for curing of epoxy resins. Resins cured with imidazoles possess excellent resistance to chemicals and to oxidation reactions, have high thermal and shape resistance and good dielectric parameters.  The courses of the reactions of the epoxides with the various derivatives of imidazole in the concentration range 0.5-25 epox. weight eq./mol imidazole and in the temperature range 80-155°C were studied. All imidazoles form adducts with epoxides very quickly, namely the 1-substituted imidazole 1: l adducts, in case of the 1,3-unsubstituted imidazoles the reaction continues to the 1:2 adducts. The polymerization effectiveness of the imidazoles falls in order 2-ethyl-4-methylimidazole (EMI) > 1-n-butylimidazole (BI) > 2-phenylimidazole (PI) > imidazole (I) » 1-vinylimidazole (VL) > benzimidazole (BZJ). In the concentration and temperature range studied the overall curing rate is directly proportional to the imidazole and epoxide concentrations and follows the Arrhenius ratio with similar values of the overall activation energy Eα = 70 to 79 kJ/mol for all active tested imidazoles in the studied concentration and temperature range [2].

Mechanism for the Reaction between Epoxy Resin and 2-PI

Young Jae Shin and coworkers formed an anisotropic conducting film (ACF) for electronic equipment applications with epoxy-imidazole resin system [3]. In this study, the curing behaviors of an epoxy resin with imidazole, 2-methylimidazole, 2-ethylimidazole, 2-phenylimidazole, 1-methylimidazole, 2-ethyl-4 (5) -methylimidazole, and 1-(2-cyanoethyl) -2-ethyl-4 (5) -methylimidazole were investigated using differential scanning calorimetry (DSC), and the curing times were determined at 150 and 180 °C. The polymerization mechanism for the epoxy resin with imidazoles was examined, and the DSC results matched the mechanism [3].

Scheme 1 The curing mechanism of 2-PI with an epoxy resin

The mechanism for the reaction between epoxy resin and 2-PI was determined in this study (scheme 1). Initially, an adduct reaction occurred between the epoxy resin and imidazoles, and then the epoxy resin was anionically polymerized from the adduction product. The curing times of the epoxy resin with imidazoles were determined using the direct indentation method at 150 and 180 °C.

References

[1] https://www.alfa.com/en/catalog/B23858/

[2] Jíšová, Václava, Curing mechanism of epoxides by imidazoles, Journal of Applied Polymer Science, Volume 34 (7), Nov 20, 1987, p2547-2558

[3] Young Jae Shin et. al., A comparison of some imidazoles in the curing of epoxy resin, Journal of Industrial and Engineering Chemistry, 16 (2010) 556–559