Synthesis of Highly Branched Alkoxysiloxane−Dimethylsiloxane Copolymers by Nonhydrolytic Dehydrocarbon Polycondensation Catalyzed by Tris(pentafluorophenyl)borane

Abstract

A new approach to the synthesis of highly branched alkoxy functionalized polysiloxanes has been developed. Dehydrocarbon polycondensation of tetraalkoxysilanes with 1,1,3,3-tetramethyldisiloxane (HMMH) catalyzed by tris(pentafluorophenyl)borane [B(C6F5)3] leads to highly branched organopolysiloxanes substituted with alkoxy groups at silicon atoms. These copolymers could be used as silanol-free hydrophobic silicone resins. Polycondensations of HMMH with tetramethoxysilane (TMOS) and with tetraethoxysilane (TEOS), catalyzed by B(C6F5)3, were studied. Use of TMOS or TEOS lead to stable, soluble, branched copolymers containing a great number of reactive alkoxy groups. Dehydrocarbon polycondensation is accompanied by a metathetic exchange of functional groups as well as cleavage of siloxane bonds adjacent to the Si−H group. Both of these reactions, as well as dehydrocarbon polycondensation, occur via the tertiary silyloxonium borate intermediate.