American Chemical Society
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Viscoelastic Behavior of the Polymerized Ionic Liquid Poly(1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonylimide))

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journal contribution
posted on 2011-10-11, 00:00 authored by Kenji Nakamura, Tatsuya Saiwaki, Koji Fukao, Tadashi Inoue
Dynamic melt viscoelastic behavior for polymerized ionic liquids, poly(1-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonylimide)) (PC2VITFSI), with various molecular weights was investigated in the frequency/temperature range from the glass to the terminal region. Viscoelastic spectra at given temperatures for PC2VITFSI with lower molecular weight were able to be well superimposed on each other to make a master curve. PC2VITFSI with a molecular weight larger than 1.4 × 105 were entangled with each other, showing a rubbery region in the master curves. However, viscoelastic spectra for PC2VITFSI with higher molecular weight (larger than 2.2 × 105) were not superimposed in the rubbery and terminal regions due to the presence of two rubbery elastic origins, i.e., chain entanglement and ionic aggregates. The presence of huge ionic aggregates was unable to be confirmed by SAXS measurements, but the formation of ion pairs between a cation and an anion was supported by the WAXS profiles. Master curves of PC2VITFSI exhibited extended shoulders in the glass–rubber transition region; these arose from the relaxation mode due to segmental motions of positively charged polymer chains affected by neighboring TFSI anions. The entanglement and critical molar mass of PC2VITFSI were determined to be 4.5 × 104 and 2.2 × 104, respectively.