STUDY OF THE PROPAGATION CENTER IN THE ANIONIC-POLYMERIZATION OF (METH)ACRYLIC MONOMERS .5. NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE MODEL DIMER IN TETRAHYDROFURAN

Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (1) as a model of the living dimer of tert-butyl methacrylate was studied in deuterated tetr ahydrofuran (THF-d(g)) solution by Li-6, Li-7, H-1 and C-13 NMR. In ag reement with earlier observations from infrared spectroscopy and with quantum chemical ab initio and semiempirical self-consistent field cal culations, 1 is shown to have a strong tendency to an intramolecular c oordination of Li to the penultimate ester carbonyl group. The competi ng linear form of 1 (with uncoordinated penultimate ester group) is sh own to exist due to its stabilization by self-aggregation to form a di mer of 1. In contrast to the monomeric form of 1, the dimer does not b ind THF into a specific solvate. Given the entropy-driven solvation at low temperatures, the occurrence of the dimeric aggregate is enhanced by higher temperature and concentration of 1. Both the cyclic and lin ear form of 1 are shown to exist in at least two different conformers and various solvation states. Their mutual exchange is several orders of magnitude slower than the anionic propagation reaction of tert-buty l methacrylate.