STUDY OF THE PROPAGATION CENTER IN THE ANIONIC-POLYMERIZATION OF ACRYLIC-MONOMERS .1. SPECTROSCOPIC STUDY OF METHYL 2-LITHIOISOBUTYRATE, ANINITIATOR FOR THE ANIONIC-POLYMERIZATION OF ACRYLIC-MONOMERS

As the simplest model for the propagation centre in the anionic polyme rization of methyl methacrylate, the solution of methyl 2-lithioisobut yrate (1) in tetrahydrofuran was studied by means of H-1, Li-6, Li-7 a nd C-13 nuclear magnetic resonance (NMR), and Raman spectroscopy at va rious concentrations and temperatures. A system of equilibria of diffe rently solvated dimeric, tetrameric and two isomeric trimeric aggregat es was found and their thermodynamic constants were established. On th e basis of the analysis of NMR chemical shifts, heteronuclear nuclear Overhauser effect correlation spectroscopy (NOESY) spectra and relaxat ion data, structures of the aggregates are suggested. The kinetics of the exchange between the aggregates and the lifetime of individual agg regates was established. The results suggest that the aggregation can interfere with initiation in the early steps of anionic polymerization of acrylics.