Binaphthol-derived phosphoric acids as efficient organocatalysts for the controlled ring-opening polymerization of γ-benzyl-l-glutamate N-carboxyanhydrides

Abstract

Despite great progress, it is still one attractive topic to explore new controlled ring-opening polymerization method to fabricate well-defined polypeptides. Considering the activation of organophosphates and the polymerization characteristics of N-carboxyanhydrides (NCA), we herein describe an effective (S)-1,1′-binaphthyl-based phosphoric acid catalytic system that mediates controlled ring-opening polymerization (ROP) of γ-benzyl-l-glutamate N-carboxy-anhydrides (BLG-NCA) with primary amines as initiator. In the presence of (S)-2,2′-dimethoxyl-1,1′-binaphthyl phosphoric acid ((S)-1e), ROP with various feeding ratios of BLG-NCA to initiator afforded poly(γ-benzyl-l-glutamate) (PBLG) with expected molecular weights (5.0–32.7 kg/mol) and relatively narrow dispersities (Mw/Mn = 1.05–1.16). The kinetics and chain extension experiments were conducted to identify that (S)-1e-catalyzed ROP of BLG-NCA in a controlled/living manner. A probable interaction between (S)-1e and the amine group of initiator/polymer chain-end was verified from 1H NMR, 31P NMR experiments. A plausible phosphate-ammonium mode catalyzing ROP of BLG-NCA was discussed.