Phosphazene bases: A new category of organocatalysts for the living ring-opening polymerization of cyclic esters

We demonstrate that: phosphazene bases, such as 2-tert-butylimino-2-diethylamino-1,3-dimethyiperhydro-1,3,2-diazaphosphorine (BEMP) and N'-tet-t-butyl-N,N,N,N',N',N-hexamethylphosphorimidic triamide (P-1-t-Bu), are active organocatalysts for the living ring-opening polymerization (ROP) of cyclic esters. Polyesters Z 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.