The effect of LiNTf₂ on the propagation rate coefficient of methyl methacrylate

In the present work we use accurate Pulsed Laser Polymerization (PLP) to measure the influence of various concentrations of lithium bis(trifluromethane) sulfonamide (LiNTf₂) on the propagation rate coefficient of methyl methacrylate (MMA). We also perform ¹H-NMR analysis to evaluate the effect of LiNTf₂ on poly(MMA) stereochemistry. Additionally, we perform high-level quantum-chemical calculations to model the interactions between Li⁺ and the MMA monomer and propagating radical. Across a broad range of concentrations, LiNTf₂ only slightly increases the isotacticity of the resultant poly(MMA). However, a significant increase in the propagation rate coefficient was noted upon addition of LiNTf₂. The magnitude of this increase was found to be dependent on the LiNTf₂ concentration and temperature. Theoretical calculations reveal the complexities associated with Lewis acid-mediated stereocontrol. On the basis of this theoretical work, we suggest that the potential stereocontrol afforded by Lewis acids is being hindered by their action as propagation catalysts though non-stereoselective binding modes. This journal is