Anomalous Thermal Characteristics of Poly(ionic liquids) Derived from 1-Butyl-2,3-dimethyl-4-vinylimidazolium Salts

Abstract

The synthesis of 1-butyl-2,3-dimethyl-4-vinylimidazolium triflate, its polymerization, and ion exchange to yield a trio of 1-butyl-2,3-dimethyl-4-vinylimidazolium polymers is described. Irrespective of the nature of the anion, substitution at the 2-position of the imidazolium moiety substantially increases the distance between the anion and cation. The methyl substituent at the 2-position also served to expose the importance of H-bonding for the attractive potential between imidazolium moiety and anions in polymers without a methyl group at the 2-position. The thermal characteristics of poly(1-butyl-2,3-dimethyl-4-vinylimidazolium) salts and corresponding poly(1-ethyl-3-methyl-4-vinylimidazolium) salts were evaluated. While the mid-point glass transition temperatures, Tg-mid, for 1-ethyl-3-methyl-4-vinylimidazolium polymers with CF3SO3−, (CF3SO2)2N− and PF6− counterions, were 153 °C, 88 °C and 200 °C, respectively, the Tg-mid values for 1-butyl-2,3-dimethyl-4vinylimidazolium polymers with corresponding counter-ions were tightly clustered at 98 °C, 99 °C and 84 °C, respectively. This dramatically reduced influence of the anion type on the glass transition temperature was attributed to the increased distance between the center of the anions and cations in the 1-butyl-2,3-dimethyl-4-vinylimidazolium polymer set, and minimal H-bonding interactions between the respective anions and the 1-butyl-2,3-dimethyl-4-vinylimidazolium moiety. It is believed that this is the first observation of substantial independence of the glass transition of an ionic polymer on the nature of its counterion.

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

“…Yang et al introduced the 1-butyl-2,3-dimethyl-4-vinyl imidazolium Y – monomers, 7 (BMM4VImY, Y – = CF 3 SO 3 – (Tf), (CF 3 SO 2 ) 2 N – (Tf 2 N), and PF 6 – ), in a thermal study to correlate T g ’s of homopolymers with different counteranions (see Section ) and with imidazolium separation distances. This study reiterates some features associated with how segmental solubilities vary dramatically as anion counterions are varied in imidazolium–anion pairs.…”

“…Yang et al prepared homopolymers of 1-butyl-2,3-dimethyl-4-vinyl imidazolium triflate, and examined how the T g varied when the triflate was anion exchanged for PF 6 – and for trifluoromethyl sulfonylimide (TFSI – ) . They concluded that the T g ’s were anomalously invariant with changes in counteranion.…”

“…Yang et al 82 The diaza-cage monomer, ADBr, 8 (1-(2-acryloyoxyethyl)azonium-4-aza-bicyclo[2.2.2]octane bromide), was derived from 2-bromoethyl acrylate and DABCO (diazabicyclo[2.2.2]octane), developed for use in forming mesoporous supports for iron oxide nanoparticles 84 and polyacrylonitrile nanoparticles 85 for catalytic and supercapacitor applications, respectively. The diaza-cage, 1,4-diazabicyclo[2.2.2]octane (triethylenediamine), was quaternized by reacting with 2-bromoethyl acrylate.…”

“…Glass Transitions. Yang et al 82 prepared homopolymers of 1-butyl-2,3-dimethyl-4-vinyl imidazolium triflate, and examined how the T g varied when the triflate was anion exchanged for PF 6…”

“…− and for trifluoromethyl sulfonylimide (TFSI − ). 82 They concluded that the T g 's were anomalously invariant with changes in counteranion. However, their representative DSC data exhibited a weak endotherm, not a glass transition.…”