Long-term thermal stability of five imidazolium ionic liquids

• Isothermal and dynamic TGA tests performed for 5 LIs under N2 and air atmospheres.
• [C4C1C1Im][OTf] has the highest dynamic thermal stability and [C2C1Im][C6SO4] the lowest one.
• Degradations higher than 80% after being 100 min at temperatures 40 °C lower than tonset were found.
• TGA stability trend: [C4C1C1Im][OTf] > [C4C1C1Im][NTf2] > [C4C1C1Im][FAP].

Thermal stability is an essential property to select the most suitable compounds for applications as high-temperature lubricants, thermal fluids and solvents for high-temperature organic reactions. Thermal stability of five imidazolium ionic liquids (ILs) was determined using a thermogravimetrical analyzer (TG). The ILs were 1-butyl-2,3-dimethylimidazolium tris(pentafluoroethyl) trifluorophosphate, 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl) imide, 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate, 1-ethyl-3-methylimidazolium ethylsulfate and 1,3-dimethylimidazolium dimethylphosphate. Onset temperatures were determined from dynamic experiments for the five ILs at scanning rate of 10 °C · min−1 under air atmosphere. Additionally, dynamic scans were carried out with nitrogen gas for two 1-butyl-2,3-dimethylimidazolium ILs, finding that onset temperatures are 14 °C higher than those obtained with air gas flow. The three 1-butyl-2,3-dimethylimidazolium ILs present the highest onset temperatures under air atmosphere. For these last ILs, isothermal scans at lower temperatures than the onset temperature, were performed in air gas flow, finding that the most stable is 1-butyl-2,3-dimethylimidazolium trifluoromethanesulfonate. Finally, for these ILs, lifetimes were also determined for several temperatures.