碱催化三聚氰胺甲醛体系中的竞争关系

通过电喷雾电离质谱仪(ESI-MS)和核磁共振碳谱(~(13)C-NMR)分析方法研究了碱催化三聚氰胺甲醛(MF)体系中三聚氰胺(M)羟甲基化机理和缩聚反应结构中的竞争关系。结果表明,MF反应体系中羟甲基化程度大于缩聚程度,OH~-离子作为催化剂参与反应,形成M氮负离子或羟甲基氧负离子中间体后参与羟甲基化和缩聚反应。由于ESI-MS中存在同分异构现象,无法清晰描述MF体系中生成桥键和醚键等结构的竞争关系;在~(13)C-NMR研究中表明甲醛(F)与M的摩尔比可以显著影响缩聚产物分布,在低F与M摩尔比条件下醚键与桥键具有明显竞争关系,随着摩尔比升高,醚键逐渐占据绝对优势。在MF体系中醚键结构一直具有优势的原因可能与π-π堆积超分子现象有关。

Study on the competitive relationships of the base-catalytic melamine formaldehyde system

The hydroxymethylation mechanism of melamine (M) and the competitive relationships of the polycondensation structure for the base-catalytic melamine-formaldehyde (MF) system were investigated via using electrospray ionization mass spectromete (ESI-MS) and 13C-nuclear magnetic resonance (13C-NMR).The results showed that,compared with the condensation products,the hydroxymethylation structures of M were dominant in the MF system.And,as a catalyst,the OH-ion was used to form the intermediates of melamine nitrogen negative ion or hydroxyl methyl oxygen negative ion which could participate in the reactions of hydroxylmethylation and condensation.Due to the isomery of the ESI-MS,it could not clearly showed the competitive relationships of the structures of bridge bonds (M-CH2-M) and ether bonds (MCH2OCH2M) in the MF system.In the study of 13C-NMR,it indicated that the F/M molar ratio has a considerable effect on the distribution of condensation products,which suggested that ethe bonds and bridge bonds have obvious competitive relationships under the condition of low F/M molar ratio,and ether bond graduallyhad the absolute advantage over bridge bonds with the increase of F/M molar ratio.In the MF system,the reason that the ether bonds were dominant may relate to the supramolecular phenomenon of π-π stacking.