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Study of the propagation centre in the anionic polymerization of (meth)acrylic monomers, 4 NMR and quantum chemical study of the initiation systems containing tert ‐butyl 2‐lithioisobutyrate and lithium tert ‐butoxide or lithium 3‐methylpentan‐3‐olate
Author(s) -
Kříž Jaroslav,
Dybal Jiří,
Janata Miroslav,
Vlček Petr
Publication year - 1995
Publication title -
macromolecular chemistry and physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.57
H-Index - 112
eISSN - 1521-3935
pISSN - 1022-1352
DOI - 10.1002/macp.1995.021961004
Subject(s) - chemistry , tetramer , polymerization , monomer , lithium (medication) , polymer chemistry , intramolecular force , relaxation (psychology) , tetrahydrofuran , intermolecular force , thermal stability , crystallography , molecule , stereochemistry , organic chemistry , polymer , medicine , psychology , social psychology , solvent , enzyme , endocrinology
In contrast to methyl 2‐lithioisobutyrate ( I ), tert ‐butyl 2‐lithioisobutyrate ( A ) in tetrahydrofuran (THF) appears to have one form only, irrespective of concentration (0,1‐0,8 mol/L) or temperature (203–273 K). According to its relaxation characteristics, this form probably is a tetramer. The results indicate, however, that about 20% of A do not provide well‐developed NMR signals and may be present as a partly organized pseudophase. A is shown to form 2:2 and 1:3 complexes with lithium tert ‐butoxide ( B ) and lithium 3‐methylpentan‐3‐olate (C) in THF in dependence on their mole ratio and partly on storage time. The 7 Li, 1 H and 13 C NMR relaxation behaviour of these complexes support their essentially tetrameric nature. Although intramolecular exchange of Li atoms in a complex appears to be rapid, intermolecular exchange of any of the components is vanishingly slow on the NMR time scale. The complexes of A with either B or C exhibit remarkable stability above 273 K, in contrast to that of A itself. The quantum chemical analysis of the complexes shows that they are held together by a cooperative system of polycentric bonds and electrostatic interactions. Thus they are not easily destroyed by thermal activation but they react readily with monomer. Implications of the results for anionic polymerization of (meth)acrylates are discussed.