Polysilsesquioxanes Through Base-Catalyzed Redistribution of Oligohydridosiloxanes

摘要

Organopolysilsesquioxanes have recently gained much interest as materials for low-K dielectrics [1],ceramic precursors [2] and photoresists [3].Typical sol-gel synthesis of polysilsesquioxanes involves the hydrolysis of organotricholorosilanes and/or organotrialkoxysilanes in the presence of acid or base catalysts and organic solvents.However,under sol-gel conditions most organotrialkoxysilanes do not afford silsesquioxane gels.This limits the range of organic functionalities that can be introduced into these hybrid organic-inorganic materials.An alternative route to polysilsesquioxanes is through oligohydridosiloxanes.Catalytic disproportionation,by titanium complexes,of linear or cyclic oligomers of methylhydridosiloxanes can lead to polymethylsilsesquioxanes [4].We have shown that disproportionation of oligomethylhydridosiloxanes can also be catalyzed by tetrabutylammonium hydroxide to yield polymethylsilsesquioxanes(scheme 1)[5].This replaces the step-growth sol-gel polymerization process of organotrialkoxysilanes,which requires solvent,stoichiometric water and produces alcohol and water condensation by-products.Tetraalkylammonium hydroxides,as catalysts,are also attractive because they readily decompose by heating above 150 °C;thus,they can be easily removed from the final materials.