Li Wei
Institute for Chemical Reaction Design and Discovery (WPI-ICReDD), Hokkaido University, Sapporo 001-0021, Japan.
J Phys Chem B. 2023 Sep 7;127(35):7624-7635. doi: 10.1021/acs.jpcb.3c03126. Epub 2023 Aug 29.
Living polymerization is an important synthetic approach to achieving precise control of synthesized polymers, which is crucial for their applications. The molecular weight distribution (MWD) prescribes the macroscopic properties of polymers and hence is a key feature to characterize polymerization. In this work, we present a systematic molecular dynamics simulation study of ideal living polymerization in bulk and surface-initiated systems based on a terminal stochastic reaction model. The evolution of polymer dispersity and MWD along with the polymerization process is examined. We demonstrate that MWD is generally well captured by the Schulz-Zimm distribution for bulk and surface-initiated systems with low grafting densities. However, as the grafting density in the surface-initiated case increases, heterogeneity in chain growth emerges due to the kinetic trapping of reactive sites, which causes the starving of short chains and the thriving of minority long chains such that a shoulder region shows up in MWD. This effect can be enhanced by kinetic compressing induced by polymerization. In addition, the interplay of bonding reaction kinetics and other kinetic properties (e.g., mass transfer and polymer relaxation) is further explored, alongside the influences of bonding probability and reactant concentration. We expect that this investigation will aid in our understanding of typical kinetic aspects of living polymerization.
活性聚合是实现对合成聚合物精确控制的一种重要合成方法，这对其应用至关重要。分子量分布（MWD）规定了聚合物的宏观性质，因此是表征聚合反应的一个关键特征。在这项工作中，我们基于末端随机反应模型，对本体和表面引发体系中的理想活性聚合进行了系统的分子动力学模拟研究。研究了聚合物分散度和MWD随聚合过程的演变。我们证明，对于低接枝密度的本体和表面引发体系，MWD通常能很好地由舒尔茨-齐姆分布描述。然而，在表面引发的情况下，随着接枝密度的增加，由于反应位点的动力学捕获，链增长中出现了不均匀性，这导致短链饥饿和少数长链的繁盛，从而使MWD中出现一个肩部区域。这种效应可以通过聚合诱导的动力学压缩来增强。此外，还进一步探讨了键合反应动力学与其他动力学性质（如传质和聚合物松弛）之间的相互作用，以及键合概率和反应物浓度的影响。我们期望这项研究将有助于我们理解活性聚合的典型动力学方面。
