COCONDENSATION OF MELAMINE AND UREA THROUGH FORMALDEHYDE

在75 MHz频率下，测定了不同合成条件下脲醛树脂、三聚氰胺甲醛树脂和三聚氰胺尿素共缩聚树脂的~（13）C NMR谱。研究了三聚氰胺与尿素通过形成亚甲基或二亚甲基醚键发生共缩合反应的可能性。在中性条件下，用标记法分析了富碳13甲醛的几个反应，确定了通过形成亚甲基或二亚甲基醚键将共缩合引入三聚氰胺-脲醛树脂体系的驱动力，并将UF树脂的亚甲基键碳信号与MF树脂的亚甲基键碳信号进行了清晰的区分。由共缩合亚甲基键的碳引起的信号可以与由UF和MF树脂引起的信号分开识别。三聚氰胺的羟甲基与尿素残基上的伯氨基反应主要形成共缩合的亚甲基键，而尿素残基上伯氨基不足时，易形成共缩合的二亚甲基醚键。可以得出结论，通过使羟甲基三聚氰胺与在伯氨基中丰富的脲或羟甲基脲反应，或者通过使脲的羟甲基与三聚氰胺的氨基反应，可以有效地引入共缩合的亚甲基键。

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.