Investigations of the chemical structure of sulfonated amino‐formaldehyde resins. I 13C‐NMR analysis of sulfonated urea‐formaldehyde resins

Abstract 13C nuclear magnetic resonance has been successfully used for the determination of the chemical structure of sulfonated urea‐formaldehyde resins. Model compounds (such as dimethylol urea and trimethylene diurea) were prepared and their NMR spectra were analyzed. The model compounds were then sulfonated and the additional signals that appeared were assigned to carbon atoms whose hydroxy groups were replaced by sulfonate groups. Urea‐formaldehyde and sulfonated urea‐formaldehyde resins were prepared and their spectra were compared and the sulfonate groups signals were identified. Using a semiquantitative approach, the relative concentrations of the main structural units were calculated and the effect of the monomer composition on the structure of the final resin was investigated.