A hyperbranched polyglycerol bearing imidazolium. tosylate units (ITHB) was synthesized through the imidazolium salt-modification of hyperbranched polyglycerol (HB). ITHB was found to possess novel reversible lower critical solution temperature (LCST)-type liquid-liquid and liquid-solid phase transition behaviors in a methanol/chloroform mixed solution The phase transition temperatures of the liquid-liquid phase transition (PTT1to2) and liquid-solid phase transition (PTT2toSus) increased with increasing the ratio of methanol in the mixed solution and decreasing the concentration of ITHB. Additionally, increasing the molecular weight of ITHB decreased the PTT values. The liquid-liquid phase transition was caused by the aggregation of ITHB, which was proved by dynamic light scattering measurement. In contrast, the liquid-solid phase transition was caused by the solvation cleavage between the imidazolium. rings and solvents, which was proved by H-1 NMR measurement. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A Polym Chem 47, 7032-7042, 2009