Ionic silsesquioxanes: Preparation, structure control, characterization, and applications

Abstract

This feature article explains the preparation, structural control, characterization, and applications of ionic silsesquioxane (SQ) polymers and oligomers. Soluble rod- and ladder-like polySQs (PSQs) containing ionic side-chain groups, i.e., ammonium, carboxylate, sulfonate, and phosphonate, were prepared by hydrolytic polycondensation of the corresponding organotrialkoxysilanes, which contain functional groups that can be converted to ionic groups during the reaction. The resulting PSQs were applied to hybridizations and other reactions. On the other hand, ammonium-functionalized polyhedral oligomeric silsesquioxanes (POSSs) were formed in higher yields with shorter reaction times when the hydrolytic condensation of organotrialkoxysilanes containing amino groups was performed with a superacid catalyst. Furthermore, size control, amorphization, and polymerization were achieved in preparing POSS derivatives using a superacid catalyst. These superacid-catalyzed hydrolytic condensation methods were also applicable to the preparation of a single-structured cyclotetrasiloxane. The superacid-catalyzed hydrolytic condensation method could also be used to prepare ionic liquids containing randomly structured oligoSQs, POSSs, and cyclic oligosiloxane frameworks.