Star-Shaped Quaternary Alkylammonium Polyhedral Oligomeric Silsesquioxane Ionic Liquids

New star-shaped quaternary ammonium (QA) polyhedral oligomeric silsesquioxane (POSS) salts based on octakis(tetraalkylammonium) POSS cations bearing alkyl chains of different length (methyl, n-butyl, and n-octyl) and differently polarizable anions [iodide, bis(trifluoromethylsulfonyl)imide, and ibuprofen] have been synthesized and characterized. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) investigations show that the nature of the cation plays a key role in determining the thermal behavior of QA POSS salts featuring the longest alkyl chains, whereas the influence exerted by anions becomes relevant for those bearing short and medium alkyl chains. All the QA POSS salts display amorphous behavior and, with the exception of octakis(trimethylpropylammonium)- and octakis(tri-n-butylpropylammonium)octasilsesquioxane iodide, may be classified as ionic liquids. Dynamic contact-angle studies reveal their hydrophilic attitude owing to the preferential orientation of the tetraalkylammonium groups at the film-water interface.