ma971369k_si_001.pdf (207.63 kB)
Study of the Propagation Center in the Anionic Polymerization of (Meth)acrylic Monomers: NMR and MNDO Study of the Complexes of Di-tert-butyl 2-Lithio-2,4,4-trimethylglutarate and of the Living Poly(tert-butyl methacrylate) Oligomers with Lithium Chloride
journal contribution
posted on 1998-04-21, 00:00 authored by C. Zune, P. Dubois, R. Jérôme, J. Kříž, J. Dybal, L. Lochmann, M. Janata, T. M. Werkhoven, J. LugtenburgInteractions of living oligomers of tert-butyl
methacrylate (tBuMA) with a Li counterion
and of the model living dimer di-tert-butyl
2-lithio-2,4,4-trimethylglutarate (A) with LiCl
(B) were studied
in tetrahydrofuran-d8
(THF-d8) solution by 7Li,
6Li, 1H, and 13C, 1D and 2D,
NMR spectroscopy. Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate is shown to form a 1:1 complex
with lithium chloride in THF. 1H,
7Li NMR results suggest that a rapid equilibrium
between free LiCl and the mixed complex takes place
when the molar ratio LiCl:lithiated dimer is higher than 1. From
13C relaxation times, a dimeric
aggregation (i.e.
A2B2)
of the complex is deduced, in full accord with MNDO calculations.
Preliminary
results are presented for living tBuMA oligomers prepared by initiation
with diphenylhexyllithium in
the presence of various amounts of lithium chloride. Fast-acquired
13C NMR spectra of the living ends
were recorded using 13C-enriched monomer added at the end
of the polymerization. Their structure is
shown to be affected by the amount of LiCl added and to correspond to
an equilibrium between free
lithium chloride and a complexed end group. A higher excess of
LiCl apparently does not change the
nature of the complexed living end. The oligomers exhibit marked
self-termination in THF at 273 K.
Finally, a correlation of the structure of the living chain ends
with the macromolecular parameters of
the resulting polymer is attempted.