三聚氰胺改性脲醛树脂化学结构及反应过程的13C-NMR研究

通过13C-NMR可以很好地解析采用传统工艺(碱-酸-碱工艺)合成三聚氰胺改性脲醛树脂反应过程中的结构变化,并可推测其发生的反应.结构分析表明:在保温反应开始阶段,尿素与甲醛之间的反应主要为加成反应,产物以一羟甲脲和二羟甲脲为主,并有少量三羟甲脲生成;三聚氰胺与甲醛的加成反应产物为一羟甲基三聚氰胺和二羟甲基三聚羟胺;缩聚反应已经发生,一羟甲脲,一羟甲基三聚氰胺,一羟甲脲与一羟甲基三聚氰胺间的缩聚反应已经开始,分子间以醚键和次甲基键连接为主.保温反应结束直到整个反应结束,缩聚反应为主要反应类型,三聚氯胺改性脲醛树脂中存在着3种反应体系:尿素甲醛的反应体系、三聚氰胺甲醛反应体系和三聚氯铵尿素甲醛共缩合反应体系.

13C-NMR Spectrometry Study on Chemistry Structures and Reaction of Melamine Modified Urea-formaldehyde Resin

The good method to analyze the structural changes of reaction process of melamine modified UF resin by the traditional process alkali-acid-alkali is ^13C-NMR. It can also extrapolate potential reaction. The structure analysis indicated that, at the beginning of heat preservation, the reaction between urea and formaldehyde was an additive reaction. Main productions are monomethylolurea and dimethylolurea besides less trimethylolurea. The additive reaction between melamine and formaldehyde produced monomethylol-melamine, dimethylol-melamine. At the same time, polycondensation occurred. The polycondensations between monomethylolurea and monomethylolurea, between monomethylol-melamine and monomethylol-melamine, and between monomethylolurea and monomethylol-melamine oc- curred too. Main connections are methenyl ether linkage and methenyl. From the end of heat preservation to the end of whole reaction, main reaction was polycondensation. In general, there were three types reaction among melamine modified UF resin, urea-formaldehyde system, melamine-formaldehyde system and melamine-urea-formaldehyde system.