LAUSR

The strong Lewis acid Al(C6F5)3, in combination with a strong Lewis base N-heterocyclic olefin (NHO), cooperatively promotes the living ring-opening (co)polymerization of lactones, represented by δ-valerolactone (δ-VL) and e-caprolactone (e-CL) in this study. Medium to high molecular weight linear (co)polyesters (Mw up to 855 kg/mol) are achieved, and most of them exhibit narrow molecular weight distributions (Đ as low as 1.02). Detailed investigations into the structures of key reaction intermediates, kinetics, and polymer structures have led to a polymerization mechanism, in that initiation involves nucleophilic attack of the Al(C6F5)3-activated monomer by NHO to form a structurally characterized zwitterionic, tetrahedral intermediate, followed by its ring-opening to generate active zwitterionic species. In the propagation cycle, this ring-opened zwitterionic species and its homologues attack the incoming monomer activated by Al(C6F5)3 to generate the tetrahedral intermediate, followed by the rate-deter...