Nitrogen-containing Curatives

A large number of commercial two-part adhesives made from liquid bisphenol A epoxies and a variety of curing agents are available. It is easier to vary the structure of these curing agents than of the epoxies. 

Primary and secondary amines add to an oxirane group to form a nitrogen-to-carbon bond which is hydrolytically stable and a beta amino alcohol which has high hydrogen bonding capability (Eq. 5). The aromatic 

Description of Mercaptan- Modified Amido Modified Modified Modified Modified Modified Aromatic Modified 

Key properties 5-Min 10-Min 45-Min 1 1 Mix Very high General Good honey- Good Useful Nylon- 

Structure of the bisphenol A moiety (4) provides stiffness, limited water solubility, and good chemical resistance. The cured adhesive thus is a stable strong matrix. 

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Room temperature latency of the nitrogen-containing curatives is typically achieved in one of two ways. One method is to employ a curative which is insoluble, or only marginally soluble, in the adhesive mixture at room temperature, but which becomes soluble at the cure temperature. The classic example of this is dicyandiamide (10). The second method is to employ a curative precursor which is inactive at room temperature, but which converts to the active curative at the cure temperature. Examples include Monuron (11) and the di-urea adduct (12) of toluene diisocyanate and dimethylamine. Full cure in one hour at about 250 F is achieved. These solid curatives are incorporated into the epoxy under high-shear conditions. Efforts to replace the water-soluble dicyandiamide with adipic dihydrazide and solid adducts of ethylenediamine such as HY-940, sold by Ciba-Geigy, have been successful. Most latent curatives typically have some activity at room temperature, which often requires the storage of the uncured adhesive at subambient temperatures. 

Nitrogen is often used to blanket prepolymers and curatives after the container has been partially used. The blanketing system, if left in place permanently, must be so engineered that the container cannot build up a level of pressure in it that renders the situation unsafe. 

Curatives. The function of curatives is to cross-link the polymer chains into a network the most common ones are the sulfur type for unsaturated rubber and peroxides for saturated polymers. Chemicals called accelerators may be added to control the cure rate in the sulfur system these materials generally are complex organic chemicals containing sulfur and nitrogen... 

A large number of investigations in acid media have led to the conclusion that the inhibition effect caused by relatively small and simple molecules is due to their adsorption on the metal surface. Compounds of this nature usually contain sulfur and nitrogen, or are of the groups of higher alkyl-alcohols and fatty acids. Typical compounds to be discussed here in more detail are quinoline and thiourea derivatives. Fig. 5 shows a comparison of the effectiveness of several such compounds determined by means of weight loss measurements on carbon steel in 5% sulfuric acid at 40° C. as a function of the inhibitor concentration. A cur-... 

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