Thermosetting alkyd, polyester and acrylic paints based on nitrogen resins

What follows must be qualified by saying that the chemistry of the nitrogen resins has not been established beyond doubt. The account presented here is therefore a simplified outline, but one which nevertheless helps the paint and resin formulator to understand the processes involved. 

U/F resins get their name from their main ingredients urea and formaldehyde. Both are soluble in water urea, a white crystalline solid melting at 133 C, to the extent of 80 g in 100 g of water, while formaldehyde is usually supplied as the 37 per cent aqueous solution, formalin , or the solid, paraformaldehyde. Paraform is the condensation homopolymer produced by evaporating formalin  

It yields formaldehyde gas when heated to 180-200C. Reactions between urea and formaldehyde proceed as follows  

The methylol group gets its name because it consists of a methyl group in which one hydrogen atom is replaced by an alcoho/ic hydroxyl. Note particularly that acid conditions give a condensation reaction, while basic conditions give an addition reaction. It is the latter route that interests us at present, because the water-soluble dimethylol urea could at this stage be converted to a water-soluble resin, by a switch to acid conditions  

Dimethylol urea has a functionality of four (two -CH2OH, two HN-), so resin formation occurs with ultimate cross-linking. The high concentration of hydroxyl groups present in the linear version of the resin means poor solubility in organic solvents. This situation can be remedied by reaction of the hydroxyl with a suitable alcohol 

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Thermosetting alkyd, polyester and acrylic paints based on nitrogen resins... 

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