Melamines

Melamine (l,3,5-triamino-2,4,6-triazine) was first prepared by Liebig in 1835. For a hundred years the material remained no more than a laboratory curiosity until Henkel patented the production of resins by condensation with formaldehyde. Today large quantities of melamine-formaldehyde resins are used in the manufacture of moulding compositions, laminates, adhesives, surface coatings and other applications. Although in many respects superior in properties to the urea-based resins they are also significantly more expensive. 

A number of methods of producing melamine have been described in the literature. These include  

It will be noted that dicyanodiamide is the dimer of cyanamide and melamine is the trimer. 

Only one melamine molecule is formed from six urea molecules, whilst three molecules of ammonia carbamate are formed. Whilst this can be recycled to urea the conversion from urea to melamine per cycle is at most 35%. Both the main route and the recycling operation involve high pressures and the low process efficiency offsets some of the apparent economic attractions of the route compared to those from dicy . 

Melamine, a non-hygroscopic, white crystalline solid, melts with decomposition above 347°C and sublimes at temperamres below the melting point. It is only slightly soluble in water 100 ml of water dissolve 0.38 g at 20°C and 3.7 g at 90°C. It is weakly basic and forms well-defined salts with acids. 

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It is manufactured by heating dicyandiamide, H2N C(NH) NH CN, either alone or in the presence of ammonia or other alkalis, in various organic solvents. Melamine is an important material in the plastics industry. Condensed with melhanal and other substances it gives thermosetting resins that are remarkably stable to heat and light. U.S. production 1980 80 000 tonnes. 

Melamine - formaldehyde polymers. Melamine (2 4 6-triamino-1 3 5-triazine), obtained by heating dicyandiamide under pressure, condenses with formalin to give melamine - formaldehyde polymers (Beetle - Melamine), which have similar uses, but better stability to heat... 

Acrylic-poly(vinyl chloride) alloy Melamine phenolic... 

The use of hydroxyethyl (also hydroxypropyl) methacrylate as a monomer permits the introduction of reactive hydroxyl groups into the copolymers. This offers the possibility for subsequent cross-linking with an HO-reactive difunctional agent (diisocyanate, diepoxide, or melamine-formaldehyde resin). Hydroxyl groups promote adhesion to polar substrates. 

The monomer used for preparing melamine formaldehyde is formed as follows ... 

Properties Melamine phenolic, woodflour- and cellulose-filled Nitrile... 

This particular representation makes it easy to visualize formaldehyde as a step-growth monomer of functionality 2. Our principal interest is in the reactions of formaldehyde with the active hydrogens in phenol, urea, and melamine, compounds [II] [IV], respectively ... 

Fig. 2. The sol—gel polymerization of resorciaol with formaldehyde (a) and (b) of melamine with formaldehyde. Reproduced from Refs. 13 and 14,...

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