Quantum-chemical (density functional theory) study of lithium 2-methoxyethoxide, methyl alpha-lithioisobutyrate, and their mixed aggregates as modelsof the active center in the anionic polymerization of methacrylates

Density functional theory calculations of stabilities of various aggregates of lithium 2-methoxyethoxide (MEO-Li), methyl alpha-lithioisobutyrate (MIB -Li), and their mixtures show that hexameric structures of prismatic type a re most stable. The calculated NMR shifts at the alpha-carbon atoms of thes e aggregates correctly reproduce the experimental dependence of the shifts on the molar ratio MEO-Li/MIB-Li. Since these mixtures are models for the a ctive center in the anionic polymerization of methyl methacrylate (MMA), it is demonstrated that some of these mixed aggregates are able to coordinate an MMA molecule. The resulting complex is very stable and has a geometry s uitable for the monomer addition reaction, i.e., the bond formation between the MIB-Li alpha-carbon and the monomer vinyl group.