The glass transition in polymers derived from tetrasubstituted 1-butyl-2,3-dimethyl-4-vinylimidazolium salts has been found to be surprisingly invariant as compared to that in polymers derived from corresponding salts of trisubstituted 1-ethyl-3-methyl-4-vinylimidazolium or disubstituted 1-ethyl-3-vinylimidazolium monomers. It is believed that this invariance is a result of greater steric separation between the tetrasubstituted imidazolium moiety and its counter anion. If this is the case, similar invariance in glass transition characteristics may be observed in polymers derived from other trisubstituted and tetrasubstituted imidazolium monomers. In the present research, new trisubstituted ionic liquid imidazolium monomers, have been synthesized. The most straight forward synthetic option for synthesis of 1-butyl-2-methyl-3-vinylimidazolium salts is alkylation of commercially available 2-methyl-1-vinylimidazole. However, given the very high price of this monomer it was necessary to synthesize this intermediate in-house. Vinylation of imidazole with acetylene is the most precedented option for the synthesis of 2-methyl-1-vinylimidazole. Unfortunately, vinylation with acetylene is not a reaction that is well-suited for execution in academic laboratories by undergraduate researchers. The aza-Markovnikov addition of 2-methylimidazole with vinylacetate to form the acetoxy imidazole derivative, 1-(2-methyl-1H-imidazol-1-yl)ethyl acetate provided an answer to this conundrum . The acetoxy derivative was pyrolized to yield 2-methyl-1-vinylimidazole from which the 1-butyl-2-methyl-3-vinylimidazolium salt was prepared. An alternative route to either 1-butyl-2-methyl-3-vinylimidazolium or 1-methyl-2-butyl-3-vinylimidazolium salts that was developed in our laboratories involved the lithiation of the 2-position of the imidazole ring in 1-vinylimidazole with subsequent methylation or butylation of the 2-lithio imidazole intermediate.

Synthesis and polymerization of new 2-substituted vinylimidazolium salts

249th National Meeting (2015)

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