Effect of solvent on the initiation mechanism of living anionic polymerization of styrene: A computational study

Abstract

For living anionic polymerization (LAP), solvent has a great influence on both reaction mechanism and kinetics. In this work, by using the classical butyl lithium-styrene polymerization as a model system, the effect of solvent on the mechanism and kinetics of LAP was revealed through a strategy combining density functional theory (DFT) calculations and kinetic modeling. In terms of mechanism, it is found that the stronger the solvent polarity, the more electrons transfer from initiator to solvent through detailed energy decomposition analysis of electrostatic interactions between initiator and solvent molecules. Furthermore, we also found that the stronger the solvent polarity, the higher the monomer initiation energy barrier and the smaller the initiation rate coefficient. Counterintuitively, initiation is more favorable at lower temperatures based on the calculated results of ΔGTS. Finally, the kinetic characteristics in different solvents were further examined by kinetic modeling. It is found that in benzene and n-pentane, the polymerization rate exhibits first-order kinetics. While, slow initiation and fast propagation were observed in THF due to the slow free ion formation rate, leading to a deviation from first-order kinetics.