碱性阶段起始F/U配比对UF最终结构影响的^(13)C-NMR研究

Study on influences of initial F/U molar ratio on final UF structure in alkaline stage by ^(13)C-NMR

采用两种工艺[如传统工艺(记为A工艺)、低起始n(甲醛或F)∶n(尿素或U)比例工艺(记为B工艺)]合成脲醛树脂(UF),并用定量13C-NMR(核磁共振碳谱)法跟踪检测UF的结构变化。研究结果表明:当碱性阶段起始n(F)∶n(U)≥2.0∶1.0时,A工艺合成的UF最终结构中亚甲基醚键含量比B工艺高11%。这是由于前者在碱性缩聚阶段中醚键生成占优势,而后者因亚甲基桥键生成参与竞争反应而使醚键含量下降,并且两者在该阶段醚键含量差异贯穿整个树脂的合成过程中。由于空间位阻效应,碱性阶段N,N′-二羟甲基脲间的反应主要生成醚键,而含游离氨基的一羟甲基脲自聚或与其他羟甲基化合物的缩聚可生成亚甲基桥键。

The urea- formaldehyde resin（UF） was respectively synthesized by two technologies[such astradition technology（namely A technology）and low initial F/U molar ratio technology（namely B technology）],andthe structure change of UF was quantitatively traced and checked by ^13C-NMR（^13C-nuclear magnetic resonance）.The research results showed that the methylene ether bond content in final UF structure synthesized by Atechnology was 11% more than that by B technology because the former had the advantage of generating ether bondin alkaline polycondensation stage,the ether bond content of the latter was decreased by competing reaction ofgenerating methylene bridge,and the difference of both ether bond contents in alkaline stage would exist in thewhole process of resin synthesis when initial F/U molar ratio was no less than 2.0∶1.0 in alkaline stage. The reactionbetween N,N′-dimethylolurea itself in alkaline stage generate mainly ether bond because of the steric hindrance,but the methylene bridge was formed by the self-condensation of monomethylolurea containing free amino or thepolycondensation between monomethylolurea and other hydroxymethyl compound.