STUDY OF THE PROPAGATION CENTER IN THE ANIONIC-POLYMERIZATION OF (METH)ACRYLIC MONOMERS - NMR AND MO LCAO STUDY OF THE INTERACTION OF DI-TERT-BUTYL 2-LITHIO-2,4,4-TRIMETHYLGLUTARATE AND THE LIVING POLY(TERT-BUTYL METHACRYLATE) OLIGOMERS WITH LITHIUM 2-(2-METHOXYETHOXY)ETHOXIDE IN TETRAHYDROFURAN

Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and th e living poly(tert-butyl methacrylate) oligomers (B) were studied in t etrahydrofuran-d(delta) at 203-273 K using H-1, C-13, Li-7, and Li-6, 1D and 2D, NMR and ab initio SCF 3-21G and MNDO quantum chemical calcu lations. LiOEEM is shown to have a strong tendency to self-aggregation , producing dimeric, trimeric, and tetrameric aggregates and competing with its mixed aggregation (or complexation) with A and, in particula r, B. When dissolved in THF, LiOEEM as well as its mixtures with A for m metastable systems which relax in several days at 258 K into equilib rium. Interaction of LiOEEM with A leads to a system of mixed aggregat es LIOEEM(1)A(1), LiOEEM(3)A(1), and possibly LiOEEM(2)A(1) along with the original components, in relative populations depending on the LiO EEM/A molar ratio, temperature, time, and probably other factors of pr eparation. Probable structures of these complexes are proposed, and th e nature of the prevalent bonding is suggested. Experimental results i ndicate that LiOEEM is unable to convert A completely at moderate exce ss (up to 4/1 mol/mol). Interaction of LiOEEM with B leads to quite an alogous complexes but with even lower yields. There appear to be trace s of uncomplexed B even at the LiOEEM/B ratio of 10 mol/mol. This is s uggested to produce at least two different kinds of active growth cent ers in the corresponding ligated anionic polymerization of tert-butyl methacrylate and, consequently, the observed bimodality of the polymer ic product. The difference with respect to methyl methacrylate, where LiOEEM ensures an almost ideal living polymerization, is suggested to be due to the steric hindrance of efficient complexation exerted by th e tert-butyl group.