Demonstration of co-polymerization in melamine–urea–formaldehyde reactions using 15N NMR correlation spectroscopy

Melamine–urea–formaldehyde resins are very important commercially, yet little is known about their structures, and the techniques that have been available to examine this are quite limited. In this manuscript we describe the use of 1H–15N HMQC NMR spectroscopy and the development of a doubly-selective 1H–15N–13C CP INEPT NMR experiment, to establish for the first time that melamine and urea co-polymerize with formaldehyde and to identify the 1H, 15N and 13C chemical shifts of the bridging units. This methodology makes it possible to examine co-condensation in industrial preparations of melamine–urea–formaldehyde resins, in order to correlate structure and function and optimize the manufacturing process.