Selective and High-yielding Preparation of Ammonium-functionalized Cage-like Octasilsesquioxanes Using Superacid Catalyst in Dimethyl Sulfoxide

Ammonium-functionalized polyhedral oligomeric silsesquioxanes (POSSs) with only cage-like octamers were selectively prepared in high yields (ca. 90%) within relatively short reaction time (7–12 h), when the hydrolytic condensations of 3-aminopropyltrimethoxysilane (APTMS), 3-(2-aminoethylamino)propyltrimethoxysilane (AEAPTMS), and an APTMS-AEAPTMS mixture, respectively, were performed using superacid trifluoromethanesulfonic acid as a catalyst in dimethyl sulfoxide at ca. 50–60 °C. The reaction was carried out in an open system to concentrate the reaction solution, followed by precipitating and washing using acetone-chloroform mixed solvent.