An ionic liquid, 1-ethyl-3-(3-ethyl-3-oxetanylmethyl) imidazolium bis(trifluoromethanesulfonyl) imide (OXIm-TFSI), was synthesized, and its cationic polymerization was examined. The heating of a mixture of 1-ethylimidazole and 3-chloromethyl-3-ethyloxetane at 90 degrees C for 48 h yielded 1-ethyl-3-(3-ethyl-3-oxetanylmethyl) imidazolium chloride, which was transformed to a room-temperature ionic liquid, OXImTFSI, by ion exchange with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI). This ionic liquid was polymerized using boron trifluoride ethyl ether complex as a catalyst to give polyOXImTFSI. Five percent weight loss temperature (T-d5) of polyOXImTFSI evaluated by thermal gravimetric analysis was 409 degrees C, indicating the high thermal stability. Glass transition temperature (T-g) of the polymer evaluated by differential scanning calorimetry was -19 degrees C, indicating the high flexibility of the material. Ionic conductivity of polyOXImTFSI was determined to be 1.86 x 10(-8) S/cm at 23 degrees C, which was far lower than that of the OXImTFSI monomer (5.05 x 10(-4) S/cm). (C) 2014 Wiley Periodicals, Inc.