Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 7. Study of the interaction of the living dimer with lithium tert-butoxide in tetrahydrofuran

✍ Scribed by Jaroslav Kříž; Jiří Dybal; Miroslav Janata; Lubomír Lochmann; Petr Vlček

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 846 KB
• Volume: 197
• Category: Article
• ISSN: 1022-1352
• DOI: 10.1002/macp.1996.021970610

✦ Synopsis

Abstract

Using ^1^H, ^6^I i, ^7^Li and ^13^C NMR, di‐tert‐butyl 2‐lithio‐2,4,4‐trimethylglutarate (A) as a dimeric model of the living poly(tert‐butyl methacrylate) is shown to form well‐defined aggregates with lithium tert‐butoxide (B) in tetrahydrofuran. The prevailing aggregates with the composition A~2~B~2~ and AB~3~ are controlled mainly by the ratio A:B. The initial mixture of aggregates is formed very fast but is metastable. Using 1D and 2D spectra, ^1^H‐^1^H and ^1^H‐^6^Li nuclear Overhauser effect and relaxations of ^1^H, ^7^Li and ^13^C, both aggregates are shown to exist mainly in three conformational forms (b, c, d) of the A‐part which are very similar in both aggregate types. In agreement with the previously published infrared spectra, form d has the γ‐ester group of A coordinated to Li. d does not exchange with the ‘open’ forms b or c with perceptible rate on the NMR time scale. Its population is promoted by a larger content of B in the aggregate. By modified neglect of differential overlap (MNDO) quantum calculations, the aggregates A~2~B~2~ and AB~3~ are predicted to have a roughly cubical core (OLi)~4~ which is distorted in the d form where one (AB~3~) or two (A~2~B~2~) Li atoms are pulled out of the cube by coordination to the γ‐ester group. The stabilization of the supramolecule A~2~B~2~ or AB~3~ and the promoting effect of B on intramolecular coordination to the γ‐ester group in A is explained in terms of a cooperative system of polycentric bonds and electrostatic interactions.