ANALYSIS ON COCONDENSATION OF MELAMINE AND UREA THROUGH C-13 ENRICHED FORMALDEHYDE WITH C-13 NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

The urea-formaldehyde (UF) resins, melamine-formaldehyde (MF) resins, and melamine-urea-formaldehyde (MUF) cocondensed resins were synthesized using the labeling method with C-13 enriched formaldehyde under neutral conditions and their C-13-NMR (nuclear magnetic resonance) spectra were analyzed. The remarkable down-field shifts by 1.2 to 2.7 ppm of the corresponding signals of UF and MUF resins were recognized by the addition of water to the DMSO-d6 solution of NMR samples. According to the results, the chemical shifts were corrected by measurements of DMSO-d6 solution free of water. The formation of cocondensed methylene linkages was induced mainly by the reaction of methylol groups of melamine and primary amino groups of urea residue, and that of cocondensed dimethylene ether linkages was apt to take place in the case of a shortage of primary amino groups of urea residue. In the reaction of methylolurea and dimethylolmelamine, methylol groups of urea residue also were found to react with the primary amino group of methylolmelamine to form cocondensed methylene linkages.