REESTIMATION OF PROPAGATION RATE CONSTANTS IN THE RADICAL POLYMERIZATION

电子自旋共振（ESR）光谱是研究自由基聚合体系基本过程的一个非常有用的工具，因为从ESR测量可以直接获得顺磁性物质的结构、浓度和动力学信息。然而，由于实验的限制，ESR光谱被认为难以获得动力学数据。幸运的是，我们发现用常规的CW-ESR光谱仪可以观察到乙烯基和二烯化合物的传播自由基的良好分辨的ESR光谱。据此，在ESR实验结果的基础上估算了乙烯基或二烯类化合物聚合的kp值，并与PLP法估算的kp值和动力学参数进行了比较。用ESR光谱法测定了甲基丙烯酸正丁酯（nBMA）在甲苯溶液中在-30 ~ 90℃范围内自由基聚合的增殖速率常数k_p。Arrhenius参数A和E_a分别为（3.40±0.4）× 10^6 M^<-1> s^<-1>和（22.0±1.0）kJ/mol。结果与脉冲激光聚合（PLP）实验结果基本一致。用ESR谱法对乙烯基单体的kp值进行了重新估计。此外，还首次在辐照下检测到氯乙烯自由基聚合过程中传播自由基的高分辨电子自旋共振（ESR）谱。用ESR谱法测定了氯乙烯自由基聚合反应的k_p值。在25℃时，氯乙烯的k_p值为（5400±1500）M^<-1> s^<-1>，这与旋转扇形法得到的结果一致。

Electron spin resonance (ESR) spectroscopy is a very useful tool to investigate fundamental processes in radical polymerization systems, because information on structures, concentrations, and dynamics of paramagnetic species can be directly obtained from ESR measurements. However, ESR spectroscopy was considered to be difficult to acquire kinetic data owing to the experimental limitation. Fortunately, we found that well-resolved ESR spectra of the propagating radicals of vinyl and diene compounds could be observed by a conventional CW-ESR spectrometer. Accordingly, kp values for the polymerization of vinyl or diene compounds were estimated on the basis of experimental results obtained from ESR measurement, and compared the obtained k_p values and kinetic parameters with those estimated by PLP method.Propagation rate constants (k_p) for the free radical polymerization of n-butyl methacrylate (nBMA) in toluene solution were measured by ESR spectroscopy in the temperature range from-30 to 90 ℃. The Arrhenius parameters A and E_a were estimated to be (3.40±0.4) x 10^6 M^<-1> s^<-1> and (22.0±1.0) kJ/mol, respectively., which were in fair agreement the corresponding data obtained from the pulsed laser polymerization (PLP). Reestimation of kp values for vinyl monomers was performed by ESR spectroscopy. Moreover, Well-resolved electron spin resonance (ESR) spectra of propagating radicals in radical polymerizations of vinyl chloride have been detected for the first time under irradiation.The value of k_p for the radical polymerization of vinyl chloride was also estimated by ESR spectroscopy. Value of k_p for vinyl chloride was (5400±1500) M^<-1> s^<-1> at 25℃, which is in agreement with one of those obtained by the rotating sector method.