Thermoplastic Silsesquioxane Hybrid Polymers with a Local Ladder-Type Structure

Abstract

Organosilsesquioxane hybrid materials are an important class of functional materials due to their tailorable functions and high thermal and optical stability. Recently, several studies showed that phenyl-substituted trialkoxysilanes can be converted into reversibly melting gels by applying hydrolysis and condensation reactions. We studied the underlying mechanisms of their formation and the final structure in detail by a combination of various spectroscopic techniques, thermal analysis, size exclusion chromatography, and X-ray diffraction. Our investigations reveal that local ladder-type silsesquioxanes with a defect-rich structure are formed in a first hydrolysis and condensation step. The partial presence of stable −OH and methoxy groups attached to the aryl-substituted silicon atoms in the ladderlike polymer explains their thermoplastic behavior. Heating above a particular consolidation temperature leads to further condensation reactions of the residual groups as well as a structural reorientation of the ladder-type polymers. The final materials are hard and cross-linked hybrid glasses with thermal stability higher than 400 °C and high optical transparency.