Epoxies nucleophilic curatives

The reactivity of epoxy groups towards nucleophilic and electrophilic species can be explained through the release of ring strain in the three member oxirane group. Nucleophilic curatives such as amines or mercaptans attack the secondary ring carbon while electrophilic curatives behave as Lewis or Bronsted acids. The epoxy ring can be opened by hydroxyl or other epoxy group aided by tertiary amines, Lewis acids or coreactants such as primary amines, mercaptans and dicarboxylic acids ... 

The reactivity of epoxy groups toward both nucleophilic and electrophilic species can most easily be explained by the release of ring strain inherent in the three-membered oxirane group. When nucleophilic curatives, such as amines or mercaptans, are used, attack occurs at the secondary ring carbon atom of the epoxy group (Eq. 1). Electrophilic curatives, such as... 

Polyfunctional aliphatic epoxy resins are generally cycloaliphatic in nature, derived from the corresponding cyclic polyolefins, for instance, (3,4-epoxycyclohexyl)methyl-3,4-epoxycyclohexanecarboxylate (3) from 3-cyclohexenylmethyl-3-cyclohexenecarJboxylate. Aliphatic epoxy resins are much more reactive toward electrophilic (acidic) curatives than are the aromatic resins, but much less reactive toward the more common nucleophilic (basic) curatives. In addition, aliphatic resins give cured products which are more brittle than those obtained from the aromatic resins. 

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... 

Epoxy adhesives get their name from the ,2-epoxy, epoxide, or oxiranc ring, which provides the reactive sites on the polymers. This three-member ring consists of two carbon atoms joined to an oxygen atom. The strained geometry contributes to the reactivity with nearly all nucleophilic compounds, not only curatives but also adherend surfaces. 

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