Superacid-catalyzed preparation of ionic polyhedral oligomeric silsesquioxanes and their properties, polymerization, and hybridization

• Published in: Journal of sol-gel science and technology 2022-12, Vol.104 (3), p.588-598
• Main Author: Kaneko, Yoshiro
• Format: Article
• Language: English
• Subjects: Ceramics; Chemistry and Materials Science; colloids; Composites; Condensates; Crosslinking; etc.; fibers; Functional groups; Glass; Hydrogels; Inorganic Chemistry; Invited Paper: Nano-structured materials (particles; Ionic liquids; Ions; Materials Science; Mixtures; Nanotechnology; Natural Materials; Open systems; Optical and Electronic Materials; Polyacrylamide; Polyamide resins; Polyhedral oligomeric silsesquioxane; Polymerization; Reaction time; Sol-Gel Research in Japan; Solvents; Triflic acid
• ISSN: 0928-0707; 1573-4846
• DOI: 10.1007/s10971-022-05821-0

This paper provides a comprehensive review of recent studies on the superacid-catalyzed preparation of ionic polyhedral oligomeric silsesquioxanes (POSSs) and their properties, polymerization, and hybridization, that have been developed by the author and co-workers so far. Octameric POSSs (T 8 -POSS) containing ammonium side-chain groups as the main products can be obtained at a high yield within a short reaction time by dissolving amino group-containing organotrialkoxysilanes in an aqueous superacid (e.g., trifluoromethanesulfonic acid) solution, followed by hydrolytic condensation by heating in an open system to evaporate the solvents. When these reactions were performed in a hydrophobic alcohol, such as 1-hexanol, a POSS mixture with a high proportion of decameric POSS (T 10 -POSS) was obtained. It was found that the proportion of T 10 -POSS can be increased by properly controlling the reaction conditions (temperature, pressure, and solvent evaporation time) using a Kugelrohr apparatus during POSS preparation in an aqueous superacid solution. Furthermore, a low-crystalline POSS and ionic liquids containing POSS components can be obtained by the superacid-catalyzed hydrolytic condensation of the mixtures of two types of organotrialkoxysilanes containing functional groups, which can be converted into ionic groups. This superacid-catalyzed hydrolytic condensation can be applied to the preparation of carboxyl-functionalized POSSs and an ammonium-functionalized specific cyclotetrasiloxane isomer. An antifogging film with a hard-coating property comprising polyamide obtained by the polycondensation of ammonium- and carboxyl-functionalized POSSs was developed as an ionic POSS application. Furthermore, using an ionic POSS and cyclotetrasiloxane as crosslinking agents, polyacrylamide hydrogels exhibiting extremely flexible and irrefrangible properties can be obtained. Graphical abstract Highlights Ionic POSSs can be obtained at a high yield within a short reaction time using superacid catalysts. The POSS size can be controlled by properly selecting the solvent type and reaction conditions. Low-crystalline ionic POSS can be obtained from a mixture of two types of organotrialkoxysilanes. Ionic liquids containing POSS components can be obtained from the mixture of two types of organotrialkoxysilanes. An antifogging film and hydrogel with flexible and irrefrangible properties were developed using ionic POSSs.