Microwave-assisted ring-opening polymerization (MROP) of trimethylene carbonate in the presence of 1-n-butyl-3-methylimidazolium tetrafluoroborate ([bmim]BF4) ionic liquid was investigated. In the presence of 5 wt % [bmim]BF4, Poly (trimethylene carbonate) (PTMC) with a number-average molar mass (M-n) of 36,400 g/mol was obtained at 5 W for only 60 min. The Mu of PTMC synthesized in the presence of [bmim]BF4 was much higher than that produced in bulk at the same reaction time. In addition, compared with those produced by conventional heating, the M-n of PTMC and monomer conversion by MROP with or without [bmim]BF4 were both higher. Thermal properties of the resulting PTMC were characterized by differential scanning calorimetry. Under microwave irradiation in the presence of ionic liquid, the polymerization could be carried out efficiently and effectively. (c) 2007 Wiley Periodicals, Inc.