Thermoplastic Silsesquioxane Hybrid Polymers with a Local Ladder-Type Structure
Svenja Pohl, Oliver Janka, Ekkehard Füglein, Guido Kickelbick
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.