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Thermoreversible Micelle Shuttle Between an Ionic Liquid and Water

Recent research from the group of Professor Tim Lodge.

Micelles formed by self-assembly of poly(ethylene oxide)-poly(N-isopropyl acrylamide) (PEO-PNIPAM) diblock copolymers transfer, intact and reversibly, from water at room temperature to the hydrophobic ionic liquid, [bmim][PF6], at elevated temperature. This "micelle shuttle" should enable the facile delivery or extraction of non-polar reagents to or from an ionic liquid reaction medium. Furthermore, because the PNIPAM core blocks come out of aqueous solution near 34 °C, and because they dissolve in the ionic liquid only above about 80 °C, this system constitutes a completely automatic and thermoreversible loading/transfer/delivery system. That is, the copolymers exist as free chains in water, but micellize on heating above 34 °C. Further heating causes the transfer into the ionic liquid, near 68 °C. Then, when heated above 80 °C, the micelles dissociate, dispensing their cargo. On cooling, the cycle is reversed.

This work was carried out by graduate student Zhifeng Bai, with help from postdoc Yiyong He and summer REU student Nick Young, under NSF support. It is described in Macromolecules, 41, 6615-6617 (2008).

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