Multi-stimuli responsive block copolymers and gels in ionic liquids

Ionic liquids (ILs) are room temperature molten salts and have attracted much attention because of their unique properties. The characteristics of ILs (non-volatility, non-flammability, chemical stability, high ionic conductivity) can contribute to high performance energy-conversion materials. On the other hand, some polymers greatly change their solubility in ILs in response to external stimuli such as temperature and light. We have found that poly($N$-isopropylacrylamide) (PNIPAm) and poly(benzyl methacrylate) (PBnMA) show upper critical solution temperature (UCST)-type phase behavior and lower critical solution temperature (LCST)-type phase behavior in an ILs, respectively. Most recently, we also discovered that certain polymers change their solubility induced by photo stimuli. In this study, we describe hierarchical self-assembly of multi block copolymer in IL. The ABC-triblock copolymer consists of PBnMA as A with a high LCST (105 $^{\circ}$C) segment, IL-compatible PMMA as B, and PPheEtMA as C with a low LCST (42 $^{\circ}$C) segment; the copolymer exhibits doubly thermo-sensitive self-assembly in IL to form an ion-gel. PBnMA and PPheEtMA (A and C) blocks are expected to aggregate at different $T_{c}$s.