In-depth analysis of radical polymerization kinetics and mechanism by highly time-resolved electron paramagnetic resonance spectroscopy in conjunction with pulsed-laser initiation

详细了解自由基聚合动力学的基础上准确的速率系数的各个步骤的增长，终止和转移是巨大的相关性的基本理解这些基本反应和模拟技术聚合过程。在我们的小组中，SP-PLP-EPR方法已经开发出来，它连接由单脉冲（SP）诱导的脉冲激光聚合（PLP）与电子顺磁共振（EPR）光谱。激光脉冲后的自由基浓度直接监测的时间分辨率为微秒至毫秒。该方法提供了完美的访问链长度依赖性的自由基终止，已被证明为甲基丙烯酸甲酯，苯乙烯和乙酸乙烯酯。由于可以监测多于一种类型的自由基的浓度，SP-PLP-EPR技术还允许研究丙烯酸酯聚合和丙烯酰胺聚合在水溶液中的终止和转移动力学。对于这些单体，在典型的聚合条件下，仲链末端自由基可以通过1，5-氢转移反应（反咬）进行内部转移，从而产生具有非常不同的动力学性质的中链自由基。几个自由基物种的分析还允许详细的动力学和机理分析的可逆失活聚合，如RAFT和ATRP. SP-PLP-EPR方法的有利的签名是由于几乎瞬时生产的小自由基的强烈突发与高灵敏度EPR检测的时间演变的自由基起源于初级光引发剂衍生的物种。该方法适用于自由基聚合的整个领域，即，所提交的项目建议书集中于SP-PLP-EPR的研究，涉及以下主题：1.本体自由基聚合反应终止速率系数的测量直到高单体转化率2。从单一SP-PLP-EPR实验推导完全和部分电离单体的自由基聚合的终止、转移和传播速率系数3。设计双脉冲PLP-EPR实验，用于测试不同链长的自由基的交叉终止模型4。测量丙烯酸酯的反咬率作为烷基酯尺寸的函数该项目旨在展示SP-PLP-EPR技术在详细和准确测量整个自由基聚合领域相关速率系数方面的巨大和无与伦比的潜力。

Detailed knowledge about radical polymerization kinetics on the basis of accurate rate coefficients for the individual steps of propagation, termination and transfer is of enormous relevance for the fundamental understanding of these elementary reactions and for the simulation of technical polymerization processes. Within our group, the SP-PLP-EPR method has been developed, which connects pulsed laser polymerization (PLP) induced by a single pulse (SP) with electron paramagnetic resonance (EPR) spectroscopy. Radical concentrations after laser pulsing are directly monitored with a time resolution of microseconds to milliseconds. The method provides perfect access to the chain-length-dependence of radical termination, as has been demonstrated for methyl methacrylate, styrene and vinyl acetate. As the concentration of more than one type of radicals may be monitored, the SP-PLP-EPR technique also allows for studies into the termination and transfer kinetics of acrylate polymerization and of acrylamide polymerization in aqueous solution. With these monomers, secondary chain-end radicals, at typical polymerization conditions, may undergo internal transfer by a 1,5-hydrogen shift reaction (backbiting) thus producing midchain radicals with very different kinetic properties. Analysis of several radical species also allows for detailed kinetic and mechanistic analyses of reversible deactivation polymerizations such as RAFT and ATRP.The favourable signature of the SP-PLP-EPR method is due to the almost instantaneous production of an intense burst of small radicals in conjunction with the highly sensitive EPR detection of the time evolution of radicals originating from the primary photoinitiator-derived species. The method is applicable within the entire field of radical polymerization, i.e., to a wide range of monomers and solvent environments.The submitted project proposal focuses on SP-PLP-EPR studies into the following topics:1. Measurement of termination rate coefficients for bulk radical polymerizations up to high degrees of monomer conversion2. Deducing termination, transfer and propagation rate coefficients for radical polymerizations of fully and partially ionized monomers from a single SP-PLP-EPR experiment 3. Design of double-pulse PLP-EPR experiments for testing cross-termination models of radicals differing in chain length 4. Measurement of the backbiting rate of acrylates as a function of alkyl ester sizeThe project aims at demonstrating the enormous and unrivalled potential of the SP-PLP-EPR technique toward the detailed and accurate measurement of relevant rate coefficients for the entire field of radical polymerization.