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

Abstract

A series of latent curing agents were developed by replacing the hydrogen atom on secondary amine in imidazole with methoxy polyethylene glycol maleate diesters via Michael addition reaction. Methoxy polyethylene glycol maleate diesters with different molecular weight also restrained the reactivity of tertiary amine in imidazole ring. The curing properties and pot-life of the modified imidazole/epoxy systems were measured by differential scanning calorimeter and rotational rheometer. The modified imidazole/epoxy system could be cured quickly at 175 C. The modified imidazole shows good latency. After stored for more than 1 month, viscosity of modified imidazole/epoxy system remains unchanged. The longer chain polyether had the better thermal latency these curing agents had. Compared with unmodified imidazole, the novel latent curing agents led to better impact strength for cured epoxy. However, the compatibility between epoxy and latent curing agent will get worse if the molecular weight of polyether unite is over 750.

Thermally Controlled Acceleration of Epoxy Resin Curing through Polymer-Bound Imidazole Derivatives with High Latency

“…Various attempts have been carried out to attain improved storage stability for imidazole derivatives. For example, encapsulation of imidazole derivatives in different polymeric or inorganic materials, as well as incorporation into inorganic networks, was described. − Also, imidazole complexes exhibiting controlled initial nucleophilicity have been reported. , Furthermore, imidazole-releasing compounds like carbonyldiimidazole or thermally sensitive Michael adducts of imidazole have been investigated. , Unfortunately, most of the accelerators known from the literature either do not show sufficient storage stability or their reactivity is highly compromised.…”

“…14,15 Furthermore, imidazole-releasing compounds like carbonyldiimidazole 16 or thermally sensitive Michael adducts of imidazole have been investigated. 17,18 Unfortunately, most of the accelerators known from the literature either do not show sufficient storage stability or their reactivity is highly compromised.…”

Synthesis of cyclotriphosphazene‐containing imidazole as a thermally latent hardener for epoxy resins and its application in carbon fiber reinforced composites

“…24 Besides, introducing substituent groups to the secondary amine ( NH) of the imidazole ring is also an effective approach to prepare latent imidazole hardeners owing to the steric hindrance effect. 4,12,[25][26][27] If the introduced substituent groups can reduce the nucleophilicity of the imidazole moiety through the electron-withdrawing effect, the curing reactivity of imidazole hardeners would be reduced, resulting in improved latency. 10 For instance, Yang et al 25 introduced the s-triazine ring to the 1-position nitrogen of the imidazole ring.…”

Solvent‐free synthesis of phosphate‐containing imidazole fluid for flame retardant one‐component epoxy resin with long pot life, low curing temperature and fast curing rate

“…11,12 Nevertheless, the high reactivity of imidazole rings with epoxy groups also resulted in poor storage stability and even curing in a few hours at room temperature. 13,14 Therefore, many methods have been proposed to solve this problem, including microencapsulation, introducing thermolabile groups (blocking the active site and releasing the imidazole group as being heated), and so forth. Jee et al 15 encapsulated the curing agent with graphene nanoplatelets (GNPs) via a dry particle coating (DPC) process.…”

“…For this reason, imidazole and its derivatives were often used to prepare one‐component EP (pre‐mixing of curing agent with epoxy prepolymer), which could improve production efficiency and meet the requirements of large‐scale industrial production 11,12 . Nevertheless, the high reactivity of imidazole rings with epoxy groups also resulted in poor storage stability and even curing in a few hours at room temperature 13,14 . Therefore, many methods have been proposed to solve this problem, including microencapsulation, introducing thermolabile groups (blocking the active site and releasing the imidazole group as being heated), and so forth.…”