REESTIMATION OF PROPAGATION RATE CONSTANTS IN THE RADICAL POLYMERIZATION

电子自旋共振(ESR)谱是研究自由基聚合体系基本过程的一种非常有用的工具，因为顺磁物种的结构、浓度和动力学信息可以直接从ESR测量中获得。然而，由于实验的限制，ESR波谱被认为很难获得动力学数据。幸运的是，我们发现用常规的CW-ESR光谱仪可以观测到乙烯类和二烯类化合物传播自由基的高分辨ESR谱。根据电子自旋共振测量的实验结果，估算了乙烯类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。在-30~90℃的温度范围内，用电子自旋共振光谱测定了甲基丙烯酸丁酯在甲苯溶液中自由基聚合的传播速率常数。阿累尼乌斯参数A和E_a分别为(3.4±0.4)×10~(-6)M^~(-1)·g~(-1)·S~(-1)·g~(-1)和(22.0±1.0)kJ/mol，与脉冲激光聚合(PLP)的相应数据符合较好。用ESR波谱重新估算了乙烯基单体的Kp值。此外，还首次测定了辐射下氯乙烯自由基聚合过程中自由基的高分辨电子自旋共振(ESR)谱，并用ESR谱估算了氯乙烯自由基聚合的kp值。在25℃时，氯乙烯的kp为(5400±1500)M^-1；-1；S^-1&gt；与旋转扇形法测得的结果一致。

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.