Inorganic silicate polymers made directly from silica using ionic liquid as ionic plasticizer: Monovalent-only system

Abstract

Novel inorganic polymers made of silicate units are synthesized through a two-step method, by which silica is first converted to silicate glass and then transformed to silicate polymers by plasticization with ionic liquid. Ionic liquid works as an ionic plasticizer which weakens the bonds between the segments, increasing the free volume of the silicate glass. The resulting materials are carbon-free (silicate-based) inorganic polymers with glass transition temperatures of as low as 150 °C, showing various characteristics of conventional organic polymers. Specifically, we have observed that silicates with large counterions are more soluble in ionic liquid, silicate polymers are amorphous, plasticization mechanism by ionic liquid is a cation exchange reaction where small K+ ions are replaced with large EMIM+ ions, which is facilitated by heating, and that during compression molding, applying pressure at higher temperature, as compared to room temperature, is needed to promote mixing between IL and silicate glass.