Ammonia-Catalyzed Phenolic Resins

These resins differ from the other resols, because there are some benzylamine bridges present in their structure. The reactions result in early losses of water and allow higher molecular weight buildups before the resins gel. Nitrogen-containing resols are darker in color than regular resols. The di benzylamine bridges form as follows [145]  

In amine or ammonia-catalyzed reactions [145], the additions and the condensations occur almost simultaneously with each other. Methylol groups are still present in the finished resins to the extent of 15-30 groups per 100 phenol residues. The structures are branched and the degree of branching depends upon the amine used. 

The overall mechanism can be shown as a special case of a Mannich reaction  

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The rate of stripping or the stripability on catalyzed urethane and epoxy resin finishes can be increased by adding formic acid, acetic acid, and phenol. Sodium hydroxide, potassium hydroxide, and tnsodium phosphate may be added to the formula to increase the stripability on enamel and latex paints. Other activators include oleic acid, trichloroacetic acid, ammonia, triethanolamine, and monoethylamine. Methylene chloride-type removers arc unique in their ability to accept cosolvcnts and activators that allow the soludon to be neutral, alkaline, or acidic. This ability greatly expands the number of coalings that can be removed with methylene chloride removers. 

Two-stage resins (novolacs) are produced by the acid-catalyzed reaction of phenol and a portion of the required formaldehyde. Tire resin product is brittle at room temperature. It can be melted, but it will not crosslink. Novolacs can only be cured by the addition of a hardener, almost always formaldehyde supplied as hexamethylene tetramine. Upon heating, the latter compound decomposes to yield ammonia and formaldehyde. 

The use of aqueous ammonia in the preparation of wood fiber filled phenolic plastic molding has been investigated. In this case ammonia both plasticizes the wood filler and catalyzes the phenolic methylol condensation. With proper formulations and treatments, it is possible to maximize the quantity of wood fiber that can be used and minimize the resin without deterioration of properties of the molded product (61). 

Melamine resins are used from this group of thermosets for the manufacture of food contact materials. The melamine can be used in mixtures with urea and in some applications with phenol (< 1 %). The polymerization process is catalyzed in the presence of organic acids (e.g. acetic acid, lactic acid, tartaric acid, citric acid), hydrochloric acid, sulfuric acid, phosphoric acid, sodium and potassium hydroxide, ammonia, calcium or magnesium hydroxide as well as salts of these substances (total < 1 %) which cause the elimination of water and lead to a cured resin system. Stearic acid can be used as a lubricant as can zinc, calcium and magnesium salts, esters of montanic acid with ethandiol and 1,3-butandiol, as well as silicone oil (total < 1 %). 

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