[en] A monomeric model structurally comparable to the active end of a living poly(methyl methacrylate) (PMMA), i.e., a methyl α-lithioisobutyrate (MIBLi)/THF solution, was studied by both Li-7 and C-13 NMR. It has been shown that two different coordination aggregates exist in a MEBLi/THF solution. That situation corresponds to a slow exchange process between tetramer and dimer, i.e. the later being favored by a decrease in temperature or concentration. Such an equilibrium is characterized with ΔH = -2.1 kcal/mol and ΔS = -13.7 cal/mol.K by means of Li-7 NMR. Again, C-13 NMR results obtained suggest that a MIBLi/THF solution displays a charge-delocalized character, which is different from a O-Li-bonded bonded structure in solid state established by crystal analyses of several similar ester enolates.
Center for Education and Research on Macromolecules (CERM)
Politique Scientifique Fédérale (Belgique) = Belgian Federal Science Policy ; Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS