高醚含量尿素-三聚氰胺-甲醛缩聚树脂合成及化学结构研究

Synthesis and Chemical Structures of High-Ether Content Urea-Melamine-Formaldehyde Resins

分别采用常规和高醚工艺合成脲醛(UF)树脂及三聚氰胺改性脲醛(UMF)树脂,研究了各树脂的基本性能及化学结构特征。高醚工艺采用甲醛/尿素为2.7的初摩尔比,在pH为3.0的酸性条件下进行缩聚反应,树脂中的线性及环状亚甲基醚键含量增加,固化时间较长,贮存稳定性好,游离甲醛含量较低;改性树脂中的三聚氰胺在反应初期加入,羟甲基化较充分,产物缩合增加了树脂中线性亚甲基醚键的含量,同时也导致尿素与甲醛羟甲基化程度下降,缩合生成亚甲基数量减少,因此树脂中剩余羟甲基含量增加。21%~27%尿素游离于低摩尔比常规UF树脂中未参与反应,而其在高醚UF树脂中含量更高。

Urea-formaldehyde and urea-melamine-formaldehyde resins were synthesized using regular and high-ether methods, respectively. The characteristics and chemical structures of these resins were studied. In high-ether method, an initial mole ratio of 2.7 was used and the polycondensation reaction was conducted at pH 3.0. The contents of linear and cyclic methylene-ether groups increased. The resins had longer curing time, better storage stability, and lower free formaldehyde content. The melamine was added in the first step of resin synthesis and was fully hydroxymethylated and then polycondensated to increase the content of linear methylene-ether groups,which however,resulted in the decrease of hydroxylmethylation between urea and formaldehyde. Therefore, the content of methylene groups decreased and the content of free hydroxylmethyl groups increased. About 21G-27G added urea did not react and remained free in the reg- ular UF resin,and the percentages were even higher in high-ether-content UF resins.