ANALYSIS ON COCONDENSATION OF MELAMINE AN D 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 synthesiz ed using the labeling method with C-13 enriched formaldehyde under neu tral conditions and their C-13-NMR (nuclear magnetic resonance) spectr a 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 t o the results, the chemical shifts were corrected by measurements of D MSO-d6 solution free of water. The formation of cocondensed methylene linkages was induced mainly by the reaction of methylol groups of mela mine and primary amino groups of urea residue, and that of cocondensed dimethylene ether linkages was apt to take place in the case of a sho rtage of primary amino groups of urea residue. In the reaction of meth ylolurea and dimethylolmelamine, methylol groups of urea residue also were found to react with the primary amino group of methylolmelamine t o form cocondensed methylene linkages.