Use of polyiminophosphazene bases for ring-opening polymerizations

The polyiminophosphazene bases Et-P-2 and t-Bu-P-4 were used as a promoter for ethylene oxide and siloxane polymerizations. Initiation by an alcohol in combination with t-Bu-P-4 lead to an extremely rapid polymerization reaction of octamethylcyclotetrasiloxane. In the case of ethylene oxide, well-defined polymers were obtained, however the rate of polymerization decreased during the polymerization reaction due to decomposition of the counterion. In combination with organolithium compounds, the phosphazene bases lead to well-defined polymers in the case of cyclotrisiloxanes as well as in the case of ethylene oxide.