Effect of lithium perchlorate on the kinetics of the anionic polymerization of methyl methacrylate in tetrahydrofuran

Abstract

The kinetics of the anionic polymerization of methyl methacrylate in the presence of lithium perchlorate (LiClO₄) are investigated in THF using 1,1-diphenylhexyllithium as initiator in a flow-tube reactor between -30 and 0 °C. The rate constants of propagation determined in the presence of LiClO₄ are lower than those obtained in the absence of the salt, similar to the effect observed for LiCl. For propagation, the reaction order with respect to active center concentration is found to be 0.5 in both cases, which indicates that LiClO₄ does not effectively perturb the aggregation of the enolate ion pair. The formation of various mixed aggregates is proposed. The polydispersity index of the obtained PMMA is lower than that obtained in the absence of salt indicating faster aggregation-deaggregation equilibria than in the absence of salt. The rate constants of termination in absence and presence of salt are comparable. Thus, LiClO₄ does not affect termination reactions, again similar to LiCl.