Catalytic Curing Agents

Catalytic curing agents initiate resin homopolymerization, either cationic or anionic, as a consequence of using a Lewis acid or base in the curing process. The Lewis acid catalysts frequently employed are complexes of boron trifluoride with amines or ethers. 

Catalytic cracking unit, 24 258-259 Catalytic curing agents, 10 388, 411-415 Lewis acids, 10 413 Lewis bases, 10 411-413 photoinitiated, 10 414-415 Catalytic cycle(s), 5 201... 

Curing agents account for much of the potential hazard associated with use of epoxy resins. There are several major types of curing agents aliphatic amines, aromatic amines, cycloaliphatic amines, acid anhydrides, polyamides, and catalytic curing agents. The latter two types are true catalysts, in that they do not participate in the curing process. 

Curing agents lhai give the optimum in elevated temperature properties for epoxy novolaks arc (hose with good high icmperaiure performance such as aromatic amines, catalytic curing agents, phenolics. and some anhydrides... 

The catalytic curing agents commonly used include tertiary amines, Lewis acids and bases, and dicyandiamide. Since their function is truly catalytic, the catalyst is added at relatively low concentrations (0 to 5% by weight) to the epoxy formulation. Homopolymerization generally requires both the presence of catalysts and elevated temperatures for the reaction to proceed. Like the polyaddition reaction, the homopolymerization reaction is accelerated by hydroxyl groups or tertiary amines. 

Tetraglycidyl ether of tetraphenolethane is an epoxy resin that is noted for high-temperature and high-humidity resistance. It has a functionality of 3.5 and thus exhibits a very dense crosslink structure. It is useful in the preparation of high-temperature adhesives. The resin is commercially available as a solid (e.g., EPON Resin 1031, Resolution Performance Polymers). It can be crosslinked with an aromatic amine or a catalytic curing agent to induce epoxy-to-epoxy homopolymerization. High temperatures are required for these reactions to occur. 

Catalytic curing agents (e g., tertiary amines) Long pot life High heat resistance Can be used as an accelerator or as the sole curative Long elevated-temperature cure Poor moisture resistance Rigid Adhesives Electrical encapsulation Laminates Powder coatings... 

The relationship between Tg and (q(E.) has been calculated from Eq. (9) for

cured resins with different e are shown in Fig. 4. The curing agents used are DETA 25), EDA 26), and DDM 8) as a diamine, succinic acid anhydride (Sue A)21) as an acid anhydride and 2-ethy 1-4-methyl imidazole (Im) 21) as a catalytic curing agent. 

Tertiary amines are commonly referred to as catalytic curing agents since they induce the direct linkage of epoxy groups to one another. The reaction mechanism is believed to be as follows ... 

Catalytic-curing agents (Lewis bases and Lewis adds) 86... 

For example, an anhydride hardener (with tertiary amine accelerator) will produce a polyester -type structure with low polarity, whereas an amine hardener will form a P-hydroxyl amine network with high polarity. Hydrogen bonding of water molecules at these sites enhances the concentration of moisture which can be absorbed. However, with catalytic curing agents, polyether stmctures of relatively low polarity will form. Since it is quite common to use mixed curing agents for composite matrices, the cured... 

Catalytic curing agents require a temperature of 200°F (93°C) or higher to react. These epoxy formulations exhibit a longer working life than the aliphatic amine cured epoxies. The exothermic reaction may be critically affected by the mass of the resin mixture. Typical materials used include piperidine, boron trifluoride ethylamine complex, and benzyl dimethyl-amine (BDMA). 

Catalytic-curing agents (Lewis bases and Lewis acids). Both Lewis bases and Lewis acids in catalytic quantities (2-4 phr) cure epoxy resins rapidly without requiring heat. Lewis bases are compounds that have a free pair of electrons such as tertiary amines while Lewis acids are compounds that can accept a pair of electrons suchasboron trifluoride. Lewis acids such as boron trifluoride are so reactive that, in addition to their being highly... 

The catalytic curing agents are a group of compoimds that promote epoxy reactions without being consumed in the process. In some of the epoxy literature, catalysts... 

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 ... 

Imidazoles such as 2-methylimidazole (2-MI) and 2-phenylimidazole (2-PI) contain both a cyclic secondary and a tertiary amine fiinctional groups and are used as catalysts, catalytic curing agents, and accelerators (124,125). They are widely used as catalysts for DICY-cured epoxies in electrical laminates. For powder coatings, 2-MI adducts of LER are often used to facilitate dispersion of the components in powder coating formulations and to enhance shelf-life. Other modified imidazoles are also commercially available. The main advantage of imidazoles is the excellent balance of pot life and fast cure. 2-PI is used to increase Tg and thermal resistance. 

Catalytic curing agents require a temperature of 200°F/93 C or higher to react. They exhibit excellent resistance to acids, alkalies, solvents, inorganic salts, and water. The maximum operating temperature is 325°F/163°C, somewhat higher than that of the amine cured epoxies. 

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