Single-Center Trifunctional Organocatalyst Enables Fast and Controlled Polymerization on N-Carboxyanhydride

Ring-opening polymerization on N-carboxyanhydrides (NCA) initiated by primary amines has been the dominantly used method to prepare polypeptides with widespread applications. However, this polymerization chemistry suffers from slow polymerization rate, limited controllability, and difficulty in preparing high molecular weight polypeptides. Herein, we develop a conjugated cationic catalyst featuring cation-dipole interaction, which remarkably enhances the reaction rate and controllability of NCA polymerization, simultaneously, to afford polypeptides in a short time with predictable molecular weights (DP = 20-500) and narrow dispersities. Experimental data and computational study altogether indicate that conjugated cationic catalysts manifest a single center with triple functions by activating C5-carbonyl on NCAs to enhance the electrophilic activity of NCA monomer, activating carbamate intermediates to accelerate decarboxylation, and moderately passivating primary amines to improve controllability. Notably, this cationic-catalyst is well recyclable while keeping excellent catalytic performance. Thus, the highly efficient cationic-catalyst strategy implies practical and promising applications, representing a new avenue of catalyst design for polymerization chemistry.