On the acid side, the products precipitated from aqueous solutions of urea and formaldehyde, or from methylolureas, are low-molecular weight methyleneureas [3]:
H2NCONHðCH2NHCONHÞnH
These contain methylol end groups in some cases, through which it is possible to continue the reaction to harden the resin.
The monomethylolureas formed copolymerize by acid catalysis and produce poly- mers and then highly branched and cured networks (Formula 2):