What is Amino Resin Technology (ART)?
Two mechanisms are proposed. In the first mechanism the polymer itself reacts with the protein or carbohydrate to form covalent methylene bridges between the polymer and the protein/carbohydrate (Figure 1). In the reverse reaction the NHR amine is protonated and then displaced by water.
Figure 1: Proposed reaction mechanism for formation of urea formaldehyde polymer
(R= acylamine, and for reaction with free amine in protein, R= protein. The same mechanism is valid with hydroxyl and sulphide nucleophiles.)
The terminal ends of the urea formaldehyde polymer can be regarded as masked aldehydes, and will be reactive towards nucleophiles like amine (from protein), hydroxyl (from carbohydrates) or sulphides (from protein). The mean molecular weight of the urea formaldehyde polymer and the degree of branching is not known.
In the second proposed mechanism urea formaldehyde acts as a reservoir for formaldehyde. The conditions in the formulation of protein with the polymer alters the equilibrium to favour depolymerising to give urea and formaldehyde, which in turn can react with a suitable nucleophile. Figure 2 gives the proposed mechanism for the formation of the urea formaldehyde polymer.
Figure 2: Proposed mechanism for the formation of urea formaldehyde polymer, and depolymerisation in reverse.
Depolymerisation is probably caused by protonation of amine by the hydroxyl group and subsequent loss of formaldehyde.