Quantum-chemical DFT calculations to interpret the effect of lithium butoxide additives on the anionic polymerization of styrene in polar solvents

For the interpretation of the effect of lithium butoxides on the rate of the styrene anionic polymerization, quantum-chemical DFT calculations of their aggregation and dissociation behavior in polar solvents were performed. The calculations showed that addition of n-BuOLi should lead to the preferable scavenging of free Li+-cations by the tetrameric THF-solvated aggregates of the alkoxide, thus increasing through the common ion effect the concentration of the free anionic PSt− sites, which are the main contributors to the rate of polymerization. In contrast, addition of t-BuOLi should mostly lead to the decrease of the concentration of the PSt− active sites which abstract Li+-cations from the tetrameric aggregate of the additive, resulting in slowing down the polymerization. These results agree with the observed effects of n-BuOLi and t-BuOLi on the polymerization rate in polar solvents like THP or THF and with the increase in the solution conductivity observed upon the addition of both lithium butoxides to the solution of PSt–Li chains.