脲醛树脂合成反应过程的FTIR研究

利用傅里叶变换红外(FTIR)光谱研究了脲醛树脂合成中不同结构形成和变化情况. 对FTIR谱图解析和分析的结果表明, 在脲醛树脂预聚物合成过程中, 随着甲醛与尿素反应的进行, 红外谱图特征峰发生有规律的变化, 酰胺II带特征峰波数逐渐低移, 有更多羟甲基、醚键和—NHCH2—结构基元形成, 固化反应使上述结构基元相应减少. 着重分析了不同甲醛与尿素摩尔比(nF/nU)下尿素与甲醛反应产物结构的变化, 随nF/nU的增加, 酰胺II带特征峰波数逐渐低移, 碱性条件下醚键和—NHCH2—结构基元明显增加, 在较强酸性条件下Uron环、亚甲基桥和羟甲基显著增加, 而—NHCH2—结构基元含量下降.

Study on the Evolvement of Structure in Synthesis of Urea-Formaldehyde Resins by FTIR

By means of Fourier transform infrared(FTIR) spectroscopy, the structure development of urea-formaldehyde (UF) resins in synthesis process was investigated, and the structural difference of reaction inter-products of urea and formaldehyde was observed in alkaline and acidic media and at different formaldehyde-to-urea molar ratios. With the reaction process of urea and formaldehyde the variation of the FTIR peaks was obvious, the amide II band frequency of FTIR spectra of UF resins shifted gradually from high to low, and more methylols, ether linkages and -NHCH2- were formed. But in the cured UF resins, the contents of methylols, ether linkages, and -NHCH2- decreased. With the increase of the formaldehyde-to-urea molar ratios from 0.5 to 3.0, the amide II band frequency also shifted gradually from high to low, and the contents of ether linkages and -NHCH2- increased in alkaline media, while in stronger acidic media the contents of Uron, methylene linkages, and methylols increased, but the content of -NHCH2- decreased.