乙二醛存在时脲醛树脂的控制性聚合现象

UREA FORMALDEHYDE POLYMERIZATION CONTROLLED BY USING GLYOXAL

考察了乙二醛存在时脲醛树脂的控制性聚合现象.聚合微球的粒径分散在1.0～14μm之间,但当乙二醛存在时粒径集中在6.5～9.0μm;控制乙二醛的用量和比例可以调整所得微球的大小、改善微球的形貌和均匀性.添加乙二醛或增加乙二醛的比例能大幅延长沉淀反应的诱导期(延长25%以上);红外分析以及XRD分析结果证明醛基总量或甲醛比例的增加都可减小聚合产物的结晶性特征;乙二醛的存在调整了脲醛树脂的成核过程或初级粒子的生长速度,推测乙二醛覆盖了聚合物的表面或表面活性位,限制了尿素甲醛的扩散反应过程.乙二醛存在时杂化过程所得氧化硅微球的粒径仅为杂化微球的20%,分析结果推测杂化微球中存在氧化硅的径向含量梯度,这种梯度是氧化硅纳米粒子的杂化和脲醛树脂的聚合速度差异造成的.

The urea formaldehyde polymerization controlled by using glyoxal was investigated. The sizes of the resin microspheres were in the range of 1.0 - 14 υm, and the size range was 6.5 - 9.0 υm in the presence of glyoxal. Sizes and morphology of the resin microspheres could be adjusted or improved with altering the aldehyde amount or glyoxal ratio in the reaction. Addition of glyoxal or increment of its ratio in the reaction significantly extend the induction time of precipitation （more than 25% longer）. Infrared and XRD analyses show that the increment of both the aldehydes or the formaldehyde proportion can reduce the crystallization characteristics of polymers. Glyoxal is able to adjust the nucleation of urea formaldehyde resin or the growth of the primary particles,it was considered that the glyoxal covered the polymer surface or the active sites,limiting the diffusion of urea formaldehyde. The average size of silica microspheres prepared under the presence of glyoxal is only 20% of that of their precursor hybrids. A radial silica content gradient in the hybrid microspheres was suggested,which might result from the rate differences between silica hybridization and urea formaldehyde resin polymerization.