COCONDENSATION OF MELAMINE AND UREA THROUGH FORMALDEHYDE

在75 MHz频率下，测定了不同条件下合成的脲醛树脂（UF）、三聚氰胺甲醛树脂（MF）和三聚氰胺脲醛树脂（MUF）的C-13核磁共振波谱。研究了三聚氰胺与尿素之间通过形成亚甲基或二亚甲基醚键是否发生缩聚。用C-13富集甲醛标记法对中性条件下的几种反应进行了分析，确定了三聚氰胺-尿素树脂体系中通过形成亚甲基或二甲基醚键引入缩聚反应的驱动力。UF树脂的亚甲基键碳信号与MF树脂的亚甲基键碳信号有明显的区别。共缩合亚甲基连接碳的信号可以与UF和MF树脂的信号分开识别。椰壳化亚甲基键的形成主要是由三聚氰胺的甲基基与尿素渣的伯胺基反应引起的，而在尿素渣伯胺基不足的情况下容易形成椰壳化二亚甲基醚键。结果表明，三聚氰胺甲基与尿素或含有丰富叔胺基的三聚氰胺甲基反应，或尿素的甲基与三聚氰胺的氨基反应，均可有效引入椰壳化亚甲基键。

The C-13 NMR spectra of urea-formaldehyde (UF) resins, melamine-formaldehyde (MF) resins and melamine-urea (MUF) cocondensed resins synthesized with various conditions were measured with a frequency of 75 MHz. It was investigated whether the occurrences of cocondensation between melamine and urea through the formation of methylene or dimethylene ether linkages can be identified or not. Several reactions using labeling method with C-13 enriched formaldehyde under neutral conditions were also analyzed to determine the driving force to introduce the cocondensation through the formation methylene or dimethylene ether linkage into melamine-urea resin system.The signals due to carbons of methylene linkages of UF resins were clearly identified from those of MF resins. the signals due to carbons of cocondensed methylene linkage could be recognized separately from those due to UF and MF resins. The formation of cocondesed methylene linkages was mainly induced 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 shortage primary amino groups urea residue. It was concluded that the effective introduction of cocondesed methylene linkages can be done either by reacting methylolmelamine with urea or methylolureas abundant in the primary amino groups, or by reacting methylol groups of urea with amino groups of melamine.