Micelle/Inverse Micelle Self-Assembly of a PEO−PNIPAm Block Copolymer in Ionic Liquids with Double Thermoresponsivity

We report a doubly thermoresponsive diblock copolymer that exhibits both an upper critical micellization temperature (UCMT) and a lower critical micellization temperature (LCMT) in ionic liquids. Dynamic light scattering and cloud point measurements are employed to investigate the micellization behavior of poly(ethylene oxide)-b-poly(N-isopropylacrylamide) (PEO−PNIPAm) in 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF₄]), 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF₄]), and their blends. In a single ionic liquid solvent, at low and high temperatures, the block copolymer self-assembles into PNIPAm-core and PEO-core micelles, respectively. The core and corona of the micelles are reversibly switchable in response to the stimulus of temperature. Using [EMIM][BF₄]/[BMIM][BF₄] blends as solvents, both the UCMTs and LCMTs can be easily tuned over a wide range of temperature by varying the mixing ratio of the two ionic liquids. Depending on the relative positions of the UCMT and LCMT, two types of doubly thermoresponsive systems (micelle−unimer−inverse micelle and micelle−copolymer aggregates−inverse micelle) can be obtained.