Critical solution behavior of poly(N-isopropyl acrylamide) in ionic liquid-water mixtures
Purnendu K Nayak1, Adam P Hathorne, Harry Bermudez
1Department of Chemical Engineering, University of Massachusetts, Amherst, MA, USA.
Abstract:
The wide diversity of room-temperature ionic liquids (ILs) presents opportunities for studying, and controlling, polymer phase behavior. We have examined the phase behavior of poly(N-isopropyl acrylamide) (PNIPAM) in imidazolium ILs and their mixtures with water. We find there is a strong influence of the IL anion; specifically, the tetrafluoroborate anion yields a complex phase diagram with both LCST and UCST-type regimes. PNIPAM is generally miscible at intermediate IL-water compositions, although this range depends on the polymer molecular weight. Solvatochromatic characterization of both neat and mixed solvents reveals a key role for the interplay between PNIPAM-IL hydrogen-bonding and ion-pairing within the IL. These results demonstrate that appropriate selection of ILs should allow for increased control over polymer phase behavior.
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