Polysiloxane–POSS systems as precursors to SiCO ceramics

Abstract In the work, two linear polysiloxanes (D 2 V and V 3 polymers) containing vinyl (Vi) groups regularly distributed along their chains were cross-linked by hydrosilylation with Si H groups containing polyhedral oligomeric silsesquioxane (POSS) molecules, namely: dimethylsiloxy-substituted octahedral oligosilsesquioxane ( Q 8 M 8 H ). The reactions were carried out at equimolar Si Vi: Si H groups ratios in methylene chloride, tetrahydrofuran and toluene in order find out the optimum solvent for achieving the highest possible polymer cross-linking levels. In toluene, cross-linking was also performed at lower reactive groups molar ratios. Investigation of the cross-linked systems allowed establishing that hydrosilylation in toluene was the most efficient. Independently of the Si Vi: Si H groups molar ratio in the starting reaction medium, D 2 V polymer reacted with Q 8 M 8 H to a higher extent than the V 3 one. In some systems, Q 8 M 8 H acted not only as a cross-linker, but also as filler. Pyrolysis of the cross-linked polymers conducted in Ar atmosphere led to formation of SiCO ceramics with high yields (63.4–85.1 wt.%). Particularly advantageous effect of incorporation of POSS molecules on ceramic yield was observed for the D 2 V polymer. SiCO materials obtained are pore- and crack-free and can be applied as chemically and thermally stable protective layers on various substrates.