Cross-linking agents polyfunctional compounds

Studies of several investigators have shown that polyfunctional thiol compounds are useful as cross-linking agents for the radiation curing of unsaturated elastomers and polymers used in graphic arts, electronics, and coating industries. Already small amounts of these compounds enhance the... 

Diglycidyl ethers of Bisphenol A cannot be cross-linked through heating alone. Chemical cross-linking agents must be added. Most commonly used compounds are tertiary amines, polyfunctional amines, and acid anhydrides. Lewis acid, phenols, and compounds like dicyandiamide, however, are also used. 

Linear polymers having functional groups can be cross-Knked using suitable polyfunctional agents. Thus cellulosic fibers (cotton, rayon) are cross-Knked by reaction of the hydroxyl groups of cellulose with formaldehyde, diepoxides, dusocyanates, and various methylol compounds such as urea-formaldehyde prepolymers, N,f/-dimethylol-N,N -dimethylene urea, and trimethylomelamine. Cross-linking imparts crease and wrinkle resistance and results in crease-resistant fabrics. 

Novolaks cannot undergo a spontaneous curing, because they are polyfunctional phenols cross-linked by methylene bridges. Therefore the curing agents must be at least bifunctional compounds. Curing can be carried out without the elimination of water with compounds that are easily converted into methylene carbonium ions for example, hexamethylene tetramine, which is widely used commercially (Urotropin, Hexa). Dihydroxy-benzyl amine and trihydroxybezyl amine structures are also formed with the elimination of ammonia, e.g.. 

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