丙烯酸聚醚聚氨酯合成反应中的氢键效应及其反应动力学研究

以红外光谱法研究了丙烯酸聚醚聚氨酯合成反应(其中有氢键效应存在)及其反应动力学。结果表明:由于丙烯酸聚氨酯分子链结构中含有-CO-O-;-NH-和-O-三种主要极性基因,导致在反应中存在明显的氢键变化。在第一步聚氨酯预聚体合成中,氢键距离R随反应进行而逐渐减小,反映出-NHCO-O-结构增加,聚集加强,氢键作用加强,并趋向稳定;其中不同结构聚氨酯预聚体氢键距离R不同:R_(MDI)>R_(HDI)>R_(TDP),链段结构中有序程度依次降低。在第二步丙烯酸聚氨酯合成中,存在明显键效应,其链段结构中有序程度较原来预聚体稳定或略有下降。在二步合成反应过程中,1/1-P_(NCO)和t之间呈现很好的线性关系,表明这两步合成均属二级反学动力学。其区别在于第一步反应速率常数(k_1)较第二步反应速率常数(k_2)小一个数量级。

A Study on Hydrogen Bonding Effects and Reaction Kinetics in Two-step Synthesis of Polyurethane Acrylates

In this paper, hydrogen bonding effects and reaction kinetics in two--step synthesisof polyurethane acrylates were investigated here by IR spectra. The results showed thatthere were three kinds of polar groups--O--CO--, -NH- and -O- in the segments ofpolyurethane acrylates (PUAs), where hydrogen bonding effects existed in thesynthesis. In the lst step synthesis of prepolyurethanes (PPUs), hydrogen bonding dis-tance R decreased gradually and tended towards a stable state at the late stage, wherehydrogen bonding effects wete strongthened by the augmentation and aggregation of--NH--CO--O-- structure. The hydrogen bonding distances R of the different structureof prepolyurethanes varied as follows: R_(MDI)> R_(HDI)> R_(TDI).In the 2nd synthesis ofPUAs, where hydrogen bonding effects also existed, the ordered properties of PUAs'structure were somewhat slightly reduced, compared with those of PPUs' structure. Instudy of reaction kinetics of two--step synthesis, the plots of 1/(1-P_(NCO)) vs. t had quitewell linear relationship, where each reaction belonged to the 2nd order in reaction kine-ties. The reaction rate constant k_1 in the 1st step synthesis was one order of magnitudesmaller than that k_2 in the 2nd step synthesis.