Epoxy adhesives primary amine curatives

Primary amine curatives are most commonly used for room temperature curing of epoxy adhesives. However, aromatic primary amines can be used as latent catalysts for one-part heat curing products (Table VI). Mixtures of bis(aminopropyl)tetraoxaspiroundecane and m-phenylenediamine or bis(aminophenyl)ether, amine, sulfoxide, or thioether have been used to cure DGEBA-type resins at two temperatures (40-100°C and 120-160°C) to give cured specimens with good fracture toughness. Aromatic primary diamines can offer improved adhesion of epoxy adhesives to metals and... 

Lewis and Bronsted acids, activate the epoxy ring toward ring opening by various nucleophilic species, most often hydroxyl or other epoxy groups (Eqs. 2-4). Both types of curatives can take the form of catalytic species, such as tertiary amines and Lewis acids, or coreactants, such as primary amines, mercaptans, and dicarboxylic acids. When the curatives are catalytic species, the properties of the cured adhesive are due primarily to the epoxy resin and the stability/activity of the catalyst in the resin under cure conditions. Coreactant curatives offer much greater latitude in choosing the final cured adhesive properties because the physical characteristics of the... 

Suitable curatives for the polysulfide-epoxy reaction include liquid aliphatic amines, liquid aliphatic amine adducts, solid amine adducts, liquid cycloaliphatic amines, liquid amide-amines, liquid aromatic amines, polyamides, and tertiary amines. Primary and secondary amines are preferred for thermal stability and low-temperature performance. Not all amines are completely compatible with polysulfide resins. The incompatible amines may require a three-part adhesive system. The liquid polysulfides are generally added to the liquid epoxy resin component because of possible compatibility problems. Optimum elevated-temperature performance is obtained with either an elevated-temperature cure or a postcure. 

Epoxide adhesives comprise epoxy resin, many of which are prepared from phenols and epichlorohydrin, for example, the diglycidyl ether of bis-phenol A or bis-phenol F usually, these resins are a mixtnre of molecular weights blended to fit the applications. The most-common cnratives for epoxy resins are polyanfines (used in stoichiometric amounts), usually a chain-extended primary aliphatic amine, for example, diethylene triamine or triethylene tetraamine or chain-extended equivalents, which react rapidly with the epoxy resin at room temperature. Aromatic amines react slowly at room temperature but rapidly at higher temperatures. Most epoxide adhesives also contain catalysts, typically, tertiary amines. Dicyanimide is the most-common curative for one-component high-temperature-cured epoxide adhesives. Mercaptans or anhydrides are used as curatives for epoxide adhesives for specialist applications, for example, for high-speed room-temperature cures or for electronic applications. A smaller number of epoxide adhesive are cured by cationic polymerization catalysed by Lewis acids photogenerated at the point of application. Lewis acid photoinitiators include diaryliodonium and triarly sulphonium salts. See Radiation-cured adhesives. 

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