分别运用传统工艺及低起始甲醛与尿素的摩尔比( F/U)工艺，并进一步分别在酸性阶段降低反应的F/U摩尔比，进行脲醛树脂的合成。借助13 C￣NMR技术，对不同工艺条件下合成的脲醛树脂的最终结构进行了定量分析，并讨论了各反应阶段的F/U摩尔比对脲醛树脂( UF)最终结构的影响。结果表明：降低碱性阶段起始的F/U摩尔比，可有效地降低最终树脂结构中醚键的含量，其中，对直链型醚键的差异较小， Uron环含量的差异较大。通过在酸性阶段加入尿素，由于尿素中的游离氨基可与体系内的羟甲基发生反应，生成大量的亚甲基桥键，因此，在酸性阶段降低F/U摩尔比可以提高树脂最终结构中亚甲基桥键含量。%Traditional technology and low initial molar ratio of urea to formaldehyde ( F/U) were applied respectively, and the F/U molar ratio at acid stage was decreased to synthesize urea￣formaldehyde ( UF) resin. The structure of final UF resin, which was synthesized with different technology, were quantitatively analyzed by using 13 C￣NMR. Meanwhile the effects of F/U molar ratios at different reaction stages on the structure of UF resin were evaluated. The results showed as follows. (1) The content of methylene ether bridges was effectivly decreased by lowering F/U molar ratio at initial alkaline stage, and the change of straight￣chain ether bridge was not obviously affected, but the concentration of Uron ring was greatly affected. ( 2) The free amino group from the added urea at acid stage and the methylol group existing in the system could form methylene bridges, so the concentration of methylene bridges in the final UF resin structure was increased by lowering the F/U molar ratio at acid reaction stage.
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