Reactive Amphiphilic Aprotic Ionic Liquids Based on Functionalized Oligomeric Silsesquioxanes

Abstract

Abstract This paper discusses a method for the synthesis of ionic liquids which are mixtures of oligomeric silsesquioxanes (OSS) of polyhedral structure and their analogs with open chains containing aprotic cationic ionic groups with different lengths of alkyl substituents and reactive hydroxyl groups in the organic shell (OSS-ILs). This method includes the quaternization reaction of OSS with tertiary amine and primary and secondary hydroxyl groups by n-bromopropane or n-bromodecane. Obtained compounds were amorphous with glass transition temperature below 0 °C. The ionic conductivity of OSS-ILs increases with decreasing the alkyl substituent length and reaches 1.4·10−3 S/cm at 120 °C. Dynamic light scattering reveals that the length of alkyl substituent of OSS-ILs affects the assembly behavior in aqueous solutions. According to atomic force microscopy images, the surface morphology of the film of OSS-IL with short substituents showed disk-like flat micelles with an average diameter of 229 ± 92 nm and height of 2 nm. OSS-IL with long substituents formed polydisperse micellar morphologies, of which a majority showed elongated, worm-like structures with an average height of 2 nm. The ability to endow ionic conductivity and to tune morphology makes these materials promising as potential polymer electrolytes for various electrochemical applications, in particular ionic sensors and energy storage devices.