Imidazole epoxy cure mechanism

Another curing mechanism is operative in the curing reaction initiated by a polymerization catalyst for epoxy ring opening, where anionic catalysts such as tertiary amines 1S-l9) and imidazols 20 21> and cationic catalysts such as amine complexes of... 

The curing mechanism of epoxy resins with imidazol was investigated. The following mecha-... 

Compared with other catalysts that homopolymerize epoxies, the imidazole offers improved thermal properties and retention of mechanical properties at more elevated temperatures. The cured resin has a heat distortion temperature between 85 and 130°C, which can be further increased by a postcure to about 160°C. 

A study has been undertaken to attempt to determine a possible mechanism for the crosslinking of an epoxy resin with phthalic anhydride using an imidazole derivative as the catalyst. In this study we have used differential scanning calorimetry (DSC) to measure the heat of reaction and time of curing process. 

The mechanism of curing of the epoxy pre-polymer using, for example, imidazole derivatives is indicated schematically by the following reactions ... 

The mechanism for organometallics and Lewis acids in phenolic or anhydride cured epoxy molding compounds are still not fully understood. Lewis bases such as imidazoles can be reacted with organic acids to form salts in order to improve latency. Imidazoles are, so far, the most widely accepted as a compatible catalyst family for encapsulating microelectronics. 

L6WiS BaS6S. Lewis bases contain an unshared pair of electrons in an outer orbital and seek reaction with areas of low electron density. They can function as nucleophilic catalytic curing agents for epoxy homopolymerization as cocuring agents for primary amines, polyamides, and amidoamines and as catalysts for anhydrides. Tertiary amines and imidazoles are the most commonly used nucleophilic catalysts. Several different mechanisms are possible ... 

In a simpler form, the mechanism of curing the epoxy resins by imidazole has been formulated recently by Heise and Martin [104-106]. 

The chemical formulae of dicyandiamide 37 and of two ureas 3-(4-chlorophenyl)-l,l-dimethylurea 38 and 3-(3,4-dichlorophenyl)-l,l-dimethylurea 39, which are accelerators frequently used in combination with 37, are drawn in Fig. 12.5. The latency of these compounds is largely due to their insolubility in the epoxy resins at 20 °C. On heating to temperatures higher than 120 °C, dicyandiamide becomes soluble and reacts slowly with the epoxy groups, so that the full cure requires temperatures around 170—180 °C. The reaction is accelerated by adding ureas 38 and 39, benzyldimethylamine 34, or various imidazoles. The mechanism of addition of dicyandiamide to an epoxy group is complex and depends on the absence or presence of a tertiary base. In the former case, Zahir proposed a reaction sequence with the formation of an... 

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