Transient catalysts for the polymerization of organosiloxanes

Abstract

Abstract A study was made of the polymerization of siloxances with transient basic catalysts. These catalysts are active as polymerization catalysts for siloxanes and will decompose rapidly to inactive products at elevated temperatures with the formation of stable polymers. Several quaternary ammonium bases were studied as polymerization catalysts. It was found that bases such as tetramethylammonium hydroxide and benzyltrimethylammonium hydroxide were efficient catalysts. Similar bases having β‐hydrogen atoms decomposed too rapidly via an elimination reaction and were not good catalysts. The polymerizations of organosiloxanes with quanternary phosphonium hydroxides were also studied. The phosphonium bases decomposed thermally in a different manner than the ammonium bases to give phosphine oxides and hydrocarbones. The most efficient transient catalysts were found to be phosphonium silanolates. Tetrabutylphosphonium silanolate was conveniently prepared in an anhydrous form and it proved to be extremely efficient for the preparation of homopolymers and copolymers of organosiloxanes.