尿素甲醛聚合反应中的沉淀现象

Precipitation Phenomenon in the Urea/Formaldehyde Polycondensation

首次研究了尿素甲醛聚合反应中的沉淀现象以及不同反应条件对沉淀产物半结晶结构特征的影响.定量分析结果显示以尿素甲醛物质的量之比1.0∶1.0为基础,增加甲醛用量沉淀产物质量减少,但当增加尿素用量时沉淀质量为一定值.根据聚合产物线型结构对应的反应计算,沉淀产物收率接近100%.改变体系酸性和反应物总量等条件也可得到类似的定量反应结果.沉淀产物中特征官能团的伸缩振动光谱随着反应条件的变化而变化.当增加甲醛用量时,官能团振动吸收强度明显减弱;增加尿素用量时吸收强度略有增加.改变体系酸性和反应物总量同样可对产物的振动光谱产生影响.这种吸收强度的变化与XRD表征所得样品结晶性变化规律完全一致,这表明尿素甲醛聚合反应中的沉淀现象是一种线型分子之间氢键相互作用引起的半结晶聚积过程.

The precipitation phenomenon and the semicrystallization characteristics of the deposition appearing in the urea/formaldehyde polycondensation were described for the first time. Quantitative analysis revealed that the deposition decreased with the amount of formaldehyde increasing, based on the reaction condition of the urea/formaldehyde molar ratio of 1.0, however, the amount kept a constant with that of the urea increasing. The percentage yield of the resulting deposition achieved 100% approximately, calculated by the reaction describing the formation of a linear urea-formaldehyde resin molecule. The similar quantitative analytic result could also be obtained as varying the reaction conditions of the acidity or the total reactant amount. FT-IR characteristics of the deposition varied with the reaction conditions. Intensity of the characteristic absorption of each functional group in the deposition molecules was weakened sharply with the amount of formaldehyde increasing in the reaction, while the absorption enhanced slightly with that of the urea doing. The similar effect was also obtained as the acidity or the total reactant amount varying. The XRD results were in agreement with the FT-IR characteristics, suggesting that the precipitation process in the urea-formaldehyde polycondensation reaction be caused by the semicrystallization of the linear polymeric molecules （[NHCONHCH2]n）, induced by the hydrogen bonding interaction between them.