Polymerization of cyclotrisiloxanes by organolithium compounds and P2‐Et base

The use of the phosphazene base P2‐Et(a) as a promoter for the anionic polymerization of hexamethylcyclotrisiloxane (D3Me) or hexaethylcyclotrisiloxane (D3Et) initiated by an organolithium compound leads to well‐defined polysiloxanes. At low conversion (< ca. 9%) the polymerization of D3Me behaves like a living polymerization, however, polymers with a narrow molecular weight distribution (M̄w/M̄n < 1.1) are obtained up to much higher conversions (ca. 70%). Kinetic data and NMR spectroscopy revealed the existence of a dynamic equilibrium between complexed and uncomplexed lithium silanolates. Below ambient temperature several different types of aggregates were indicated. The occurrence of an acceleration was observed after ca. 9% conversion.