Controlled metal-free polymerization toward well-defined thermoresponsive polypeptides by polymerization at low temperature

Recent Advances and Future Developments in the Preparation of Polypeptides via N-Carboxyanhydride (NCA) Ring-Opening Polymerization

Polypeptides have the same or similar backbone structures as proteins and peptides, rendering them as suitable and important biomaterials. Amino acid N-carboxyanhydrides (NCA) ring-opening polymerization has been the most efficient strategy for polypeptide preparation, with continuous advance in the design of initiators, catalysts and reaction conditions. This Perspective first summarizes the recent progress of NCA synthesis and purification. Subsequently, we focus on various initiators for NCA polymerization, catalysts for accelerating polymerization or enhancing the controllability of polymerization, and recent advances in the reaction approach of NCA polymerization. Finally, we discuss future research directions and open challenges.

Precision Synthesis of Polypeptides via Living Anionic Ring-Opening Polymerization of N-Carboxyanhydrides by Tri-thiourea Catalysts

The chemistry of α-amino acid N-carboxyanhydrides (NCAs) has a history of over 100 years, but precise and efficient ring-opening polymerization methods for NCAs remain highly needed to facilitate the studies of polypeptides─that is, mimics of natural proteins─in various disciplines. Moreover, the universally accepted NCA polymerization mechanisms are largely limited to the "amine" and the "activated monomer" mechanisms, and the anionic ring-opening polymerization of NCAs has so far not been invoked. Herein, we show an unprecedented anion-binding catalytic system combining tripodal tri-thiourea with sodium thiophenolate that enables the fast and selective anionic ring-opening polymerization of NCAs. This method leads to the precision construction of various polypeptides with living polymerization behavior and is evidenced by narrow molecular weight distributions (M_w/M_n < 1.2), chain extension experiments, and minimal "activated monomer" pathway. Calculations and experimental results elucidate a living anionic polymerization mechanism, and high selectivities for monomer propagation relative to other deleterious side reactions, such as the "activated monomer" pathway, are attributed to the enhanced stabilization of the propagating carbamate anion, which is enforced by an intramolecular hydrogen bond within the tri-thiourea structure.

Amino-functionalized poly(N-vinylcaprolactam) derived from lysine: a sustainable polymer with thermo and pH dual stimuli response

Lysine, a renewable feedstock with economic feasibility, was tactfully cyclized to its corresponding cyclic lysine and then subjected to a reaction with acetylenes to yield a sustainable N-vinylcaprolactam (VCL) derivative. Well-defined PVCL with pendent amino groups was prepared via MADIX/RAFT polymerization.