Phosphazene Bases:  A New Category of Organocatalysts for the Living Ring-Opening Polymerization of Cyclic Esters

Abstract

We demonstrate that phosphazene bases, such as 2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine (BEMP) and N‘-tert-butyl-N,N,N‘,N‘,N‘ ‘,N‘ ‘-hexamethylphosphorimidic triamide (P1-t-Bu), are active organocatalysts for the living ring-opening polymerization (ROP) of cyclic esters. Polyesters prepared through this organocatalytic route possess predictable molecular weights, narrow polydispersities, and high end-group fidelity. Mechanistic studies suggest that the intermolecular hydrogen bonding of the alcohol initiator to phosphazene bases activates the alcohol for ROP of cyclic esters.