An upper critical solution temperature (UCST)-type phase separation in water was achieved using well-defined polymeric ionic liquids (ILs) with imidazolyl groups in their side chains, prepared based on living cationic polymerization using a cationogen/Et_1.5AlCl_1.5 initiating system with 1,4-dioxane as an added base. Aqueous solutions of the polymers with tetrafluoroborate as counteranions showed sharp and reversible UCST-type phase separation at 5–15 °C. The effect of polymer concentration, chain-end groups, and molecular weight on the phase separation temperature suggests that the phase separation resulted from interpolymer electrostatic interactions. Other polymeric ILs with SbF₆^– also showed a lower critical solution temperature-type phase separation in various organic solvents.

Alkyl vinyl ethers and isobutylene oxide were concurrently copolymerized through cationic vinyl addition and ring opening using B(C₆F₅)₃ as a catalyst. NMR analyses and acid hydrolysis of the products demonstrated that the copolymerization successfully proceeded through crossover reactions between vinyl and cyclic monomers to yield multiblock-like copolymers. Appropriate catalyst and monomer combinations with suitable reactivities were key for copolymerization.