聚乙烯醇改性脲醛树脂化学结构及反应的13C-NMR研究

通过13C-NMR解析了采用传统工艺(碱-酸-碱工艺)合成聚乙烯醇改性脲醛树脂反应过程中的结构变化,并推测其反应.结果表明:碱性条件下,甲醛与尿素以加成反应为主,反应生成大量的-羟甲脲,尿素全部参与反应,甲醛此时以聚合状态存在,同时也有缩聚反应的发生;酸性阶段以缩聚反应为主,形成以亚甲基键或醚键连接大分子体系,聚合状态的甲醛已全部分解,并以甲二醇的形式参与缩聚反应;第3次尿素的加入明显地降低了反应体系中的游离甲醛含量,同时生成物主要为-羟甲脲.聚乙烯醇单体的化学结构在13C-NMR上有较好的表征,但可以证明有聚乙烯醇缩甲醛生成的化学位移未被检测到,因此在该实验范围内,没有聚乙烯醇缩甲醛生成.

13C-NMR Spectrometry Study on Chemistry Structure and Reaction of Polyvinyl Alcohol Modified Urea-formaldehyde Resin

The very good method to analyze the structural change of reaction process of polyvinyl alcohol modified UF resin by the traditional process alkali-acid-alkali is 13C-NMR,and which extrapolate a possibly reaction.The structure analysis indicated that,under alkalinity condition,addition reaction was primary,reaction production was mainly monomethylolurea,the urea participated in the reaction completely,the formaldehyde was still in existence by polymerization,at the same time polycondensation reaction also happened.At a acid reaction stage,the polycondensation reaction was primary,the macro-molecule system was formed with the methylene or the ether linkage,the polymerization formaldehyde decomposed completely,and as the form of methylene glycol participated in condensation reaction.The third urea joined might obviously reduce the free formaldehyde content of the reacting system,the reaction production was mainly monomethylolurea.The polyvinyl alcohol monomer chemical constitution had the good attribute on 13C-NMR,but the chemical shift that proved the polyvinyl formal didn't examine,therefore in this experiment,the polyvinyl formal hasn't been product.