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合成了4,4’-二甲氧基二苯基氮氧自由基(DMDPN)和相应的烷氧基胺引发剂,用于甲基丙烯酸甲酯(MMA)的氮氧自由基调控聚合,研究了聚合过程中的动力学机理.通过电子自旋共振(ESR)表征,测定了DMDPN型烷氧基胺引发剂在100~120?C范围内的解离速率常数kd0,结果表明kd0符合阿伦尼乌斯公式(k=Ae-Ea/RT),其活化能Ea为135.2 k J·mol-1,指前因子A为3×1014.测定了末端官能团化聚合物PMMA-DMDPN的解离速率常数kd,由于DMDPN中胺氧基团周围的空间位阻较小,受到前末端效应的影响较弱,kd仅为kd0的6倍.采用间接法测定了110?C时增长自由基和DMDPN的结合速率常数kc,并绘制了该温度下MMA/DMDPN聚合体系的Fischer相图,结果表明该聚合体系对应的kd和kc值处于相图的可控/“活性”区域内.
4,4’-Dimethoxydiphenyloxide free radical (DMDPN) and the corresponding alkoxyamine initiator were synthesized for nitroxide-mediated polymerization of methyl methacrylate (MMA) The kinetic mechanism of the polymerization process was investigated by means of electron spin resonance (ESR). The dissociation rate constant kd0 of DMDPN alkoxyamine initiator in the range of 100 ~ 120? C was determined. The Nius equation (k = Ae-Ea / RT) showed an activation energy Ea of 135.2 kJ · mol -1 and a pre-exponential factor A of 3 × 1014. The dissociation rate of terminal functional group-terminated polymer PMMA-DMDPN The constant kd, due to the small steric hindrance around the amine oxygen groups in DMDPN, is less affected by the front end effect, and the kd is only 6 times that of kd0. The free radical and DMDPN at 110? Combining the rate constant kc and the Fischer phase diagram of the MMA / DMDPN polymerization system at this temperature, the results show that the corresponding kd and kc values of the polymerization system are in the controllable / active region of the phase diagram.