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-coremicelles, respectively. The core and corona of themicelles are reversibly switchable in response to the stimulus of temperature. Using [EMIM][BF₄]/[BMIM] [BF₄] blends as solvents, both theUCMTs andLCMTscan be easily tuned over a wide range of temperature by varying themixing ratio of the two ionic liquids.Depending on the relative positionsof theUCMTandLCMT, twotypes of doubly thermoresponsive systems (micelle-unimerinverse micelle and micelle-copolymer aggregates-inverse micelle) can be obtained.