October 18, 2012
Rochester Institute of Technology, Chemistry Department
Polyionic Liquids Derived from New 4-Vinylimidazolium Monomers
A robust process for the synthesis of 1-ethyl-3-methyl-4-vinylimidazolium triflate has been developed. This new monomer was synthesized in a pure, dry (water-free) state by direct alkylation of 1-methyl-5-vinylimidazole. Trends in the glass transition characteristics of the various salts of 4-vinylimidazolium and 1-vinylimidazolium polymers are similar, with the glass transition temperatures of poly(4-vinylimidazolium) BF4-, PF6-,AsF6-,and, CF3SO3- salts being significantly higher than those of the corresponding poly(1-vinylimidazolium) salts. This difference and the increase in Tg in going from BF4- to AsF6- in the 4-vinylimidazolium series is attributed to enhanced intramolecular bridging between imidazolium moieties positioned 1,3 or 1,5 along the polymer chain. It is likely that the lower glass transition temperatures of the 4-vinylimidazolium polymers with TFSI and C2N3- anions is a result of plasticization by large solvating anions, which, because of their soft nucleophilic character, allows for association between anion and cation over a larger distance.