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Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 5. Nuclear magnetic resonance study of the model dimer in tetrahydrofuran

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

Publisher
John Wiley and Sons
Year
1995
Tongue
English
Weight
450 KB
Volume
196
Category
Article
ISSN
1022-1352

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✦ Synopsis

Abstract

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 tetrahydrofuran (THF‐d~8~) solution by ^6^Li, ^7^Li, ^1^H and ^13^C NMR. In agreement with earlier observations from infrared spectroscopy and with quantum chemical ab initio and semiempirical self‐consistent field calculations, 1 is shown to have a strong tendency to an intramolecular coordination of Li to the penultimate ester carbonyl group. The competing linear form of 1 (with uncoordinated penultimate ester group) is shown to exist due to its stabilization by self‐aggregation to form a dimer of 1. In contrast to the monomeric form of 1, the dimer does not bind 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 linear 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‐butyl methacrylate.

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