Synthesis of sulfonic acid-containing POSS and its filler effects for enhancing thermal stabilities and lowering melting temperatures of ionic liquids†
To improve the thermal stability and lower the melting temperature of ion salts for using as ionic liquids (ILs), we designed an efficient filler based on octa-substituted polyhedral oligomeric silsesquioxane (POSS). Accordingly, the sulfonic acid-presenting POSS showed superior properties as a filler for improving thermal properties of ILs. In this report, initially the synthetic procedure for the sulfonic acid POSS is illustrated. We found that the POSS filler has good dispersibility in the ion salts, providing the series of homogeneous mixtures with various types of ion salts or ILs. Next, it is indicated that the degradation temperatures of the ion salts were significantly elevated by adding the POSS filler. Moreover, lowering effects on the melting temperatures were observed. In particular, we can demonstrate the transformation of ion salts to ILs by mixing with a small amount of the POSS filler. The data on the thermodynamic parameters during the melting process suggest that the symmetrical structure of the silica cube and the disturbance of the crystalline formation by POSS should contribute to the modulation of thermal properties of the ion salts.