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

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