Modes of Interaction in Binary Blends of Hydrophobic Polyethers and Imidazolium Bis(trifluoromethylsulfonyl)imide Ionic Liquids

CL Bentley and M Chwatko and BK Wheatle and AA Burkey and A Helenic and O Morales-Collazo and V Ganesan and NA Lynd and JF Brennecke, MACROMOLECULES, 53, 6519-6528 (2020).

DOI: 10.1021/acs.macromol.0c01155

Lower critical solution behavior in binary blends of hydrophobic polyethers with 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ahmimTf2N) exhibited a difference in lower critical solution temperature (LCST) greater than 80 degrees C between structurally homologous poly(isopropyl glycidyl ether) (PiPGE) and poly(n-butyl glycidyl ether) (PnBGE). Replacement of the acidic hydrogen on the imidazolium ring with a methyl group (i.e., 2,3-dimethyl-1-hexyl-imidazolium bis(trifluoromethylsulfonyl)imide (hmmim Tf2N)) significantly reduced the LCST of both the PnBGE/ionic liquid (IL) mixture and the PiPGE/IL mixture. Differing degrees of hydrogen bonding between the polymer and the cation cannot alone explain the observed behavior. Similar hydrogen bonding between the hmim(+ )cation and both polymers from molecular dynamics simulations was consistent with this conclusion. However, stronger hmim(+) cation tail/polymer alkyl side-chain interactions for PnBGE, with consequently stronger cation/anion interactions, point to solvophobic interactions as the basis for the large LCST difference between the PnBGE/hmimTf2N and PiPGE/hmimTf2N blends.

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