Abstract
The reaction of phenyl glycidyl ether (PGE) with 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium thiocyanate to initiate the polyetherification reaction was examined using thermal and spectral analysis techniques. The influence of the nucleophilicity of the anions on the deprotonation of the 1-ethyl-3-methylimidazolium cation determined the reaction pathway. The thermal degradation of the ionic liquid liberated the acetate ion and led, subsequently, to the deprotonation of the acidic proton in the imidazole ring. Thus, polymerisation of PGE occurred via a carbene intermediate. The more nucleophilic thiocyanate anion was not sufficiently basic to deprotonate the 1-ethyl-3-methylimidazolium cation, and thus proceeded through direct reaction with the PGE, unless the temperature was elevated and a competing carbene mechanism ensued.
Highlights
Imidazoles are very effective initiators for the polymerisation of epoxy resins [1,2] as they catalyse the homopolymerisation of the highly-strained oxirane group
We have previously examined the nature of the initiation of diglycidyl ether of bisphenol A
Nuclear magnetic resonance (NMR) spectroscopy revealed a significant difference in the initiation mechanisms involved in the polymerisation of phenyl glycidyl ether (PGE) when initiated with 1-ethyl-3-methylimidazolium acetate and
Summary
Imidazoles are very effective initiators for the polymerisation of epoxy resins [1,2] as they catalyse the homopolymerisation of the highly-strained oxirane (epoxide) group. This reaction occurs at comparatively low temperatures to produce polyethers that are less highly crosslinked and, more resilient [3] than some of their polyamine-cured counterparts [4]. Imidazole-cured epoxy resins display a variety of attractive thermal, mechanical, and electrical properties [5,6,7,8,9] These initiators have attracted interest from commercial producers of adhesives and anti-corrosion coatings [10,11]. The current work examines the relationship between the initiation mechanism and the nucleophilicity of the ionic liquid through the use of a model epoxide, phenyl glycidyl ether, in a detailed spectroscopic study
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