Uses
Hexamethylolmelamine can further condense in the presence of an acid catalyst; ether linkages can also form (see “Urea Formaldehyde”). A wide variety of resins can be obtained by careful selection of pH, reaction temperature, reactant ratio, amino monomer, and extent of condensation. Liquid coating resins are prepared by reacting methanol or butanol with the initial methylolated products. These can be used to produce hard, solvent-resistant coatings by heating with a variety of hydroxy, carboxyl, and amide functional polymers to produce a cross-linked film.
Preparation
To a resin flask equipped with a mechanical stirrer and condenser are added 37.8 gm (0.3 mole) of melamine and 195 gm of 37% (2.4 moles) formaldehyde solution. The pH of the mixture is adjusted with caustic to pH 8.3. The reaction mixture is heated on a water bath with stirring at 50°C for about 70-80 min, at which time all the melamine has gone into solution. On cooling the product separates as a thick white precipitate and is filtered to afford the monohydrate (after drying at 50°C). Yield: 62.5-69.0 gm (68-75%), m.p. 147°-153°C.
Preparation of Hexamethylolmelamine
NOTE: Approximately one-third of the product melts at 120°-140°C.
This reaction can also be carried out at room temperature over a two week period to give a quantitative yield, m.p. 150°-154°C. Infrared absorption data (KBr) are (microns): 2.93 (s), 3.37 (w), 6.40 (s), 6.65 (m), 6.90 (w), 7.20 (m), 7.50 (w), 7.82 (s), 8.35 (w), 10.10 (s), 10.90 (w), 11.45 (w), 12.30 (w) (where s = strong, m = medium and w = weak).
