Preparation of imidazolium-type ionic liquids containing silsesquioxane frameworks and their thermal and ion-conductive properties

An ionic liquid containing a random-structured oligosilsesquioxane (Im-Random-SQ-IL) was successfully prepared by the hydrolytic condensation of 1-methyl-3-[ 3-(triethoxysilyl) propyl] imidazolium chloride (MTICl) in aqueous bis(trifluoromethanesulfonyl) imide (TFSI). Im-Random-SQ-IL exhibited a glass transition temperature (T-g) at -25 degrees C as indicated by an endothermic peak in the differential scanning calorimetry (DSC) curve. In addition, fluidity was visually observed at ca. 0 degrees C, i.e. Im-Random-SQ-IL is a room temperature ionic liquid. Conversely, when the hydrolytic condensation of MTICl was performed using a water/methanol (1 : 19 v/v) solution of TFSI, an ionic liquid containing a cage-like oligosilsesquioxane (Im-Cage-SQ-IL) was obtained. The T-g of Im-Cage-SQ-IL was -22 degrees C, and its melting temperature (T-m) was 105 degrees C according to the DSC analysis. In addition, fluidity was observed for this ionic liquid at ca. 100 degrees C. These results suggest that both the amorphous structure of Im-RandomSQ- IL and the type of substituent groups in the silsesquioxane contributed to the ionic liquid behaviour below room temperature. In addition, these ionic liquids exhibited high thermal stabilities (Im-RandomSQ- IL: T-d3 = 429 degrees C, T-d5 = 437 degrees C and T-d10 = 447 degrees C, Im-Cage-SQ-IL: T-d3 = 427 degrees C, T-d5 = 436 degrees C and T-d10 = 446 degrees C) and relatively high ion conductivities (10(-4) -10(-3) S cm(-1), at similar to 100 degrees C).