title: Critical solution behavior of poly(N-isopropyl acrylamide) in ionic liquid-water mixtures.
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.
authors.affiliation: Department of Chemical Engineering, University of Massachusetts, Amherst, MA, USA.
authors.forename: Purnendu K
authors.initials: PK
authors.lastname: Nayak
authors.forename: Adam P
authors.initials: AP
authors.lastname: Hathorne
authors.forename: Harry
authors.initials: H
authors.lastname: Bermudez