Iron Tris(dibenzoylmethane−polylactide)

Abstract

The polymeric metal complex iron tris(dibenzoylmethane-polylactide), Fe(dbmPLA)3, was synthesized from d,l-lactide and Fe(dbmOH)3, a hydroxyl functionalized metalloinitiator. Reactions are fast relative to those with the dbmOH ligand initiator even when no Sn(oct)2 or DMAP catalyst is added, indicating that iron serves as both a dbm protecting group and a catalyst for lactide ring-opening polymerization (ROP). Kinetics experiments show good molecular weight control to ∼60−70% conversion (e.g., PDIs < 1.1; no evidence of transesterification via 1H NMR spectroscopic analysis; continued chain growth when Fe(dbmPLA)3 is heated with additional lactide monomer). For comparison, Fe(bdk)3 (bdk = β-diketonate) complexes were tested as lactide ROP catalysts using dbmOH and benzyl alcohol as the initiators. The red-orange Fe(dbmPLA)3 polymers were analyzed by GPC, 1H NMR and UV-vis spectroscopy. Demetalation with dilute HCl yields dbmPLA macroligands for chelation to other metals. The polymerization mechanism using ...