Closed-Loop CO2-Mediated Ultrafast and Controlled Synthesis of Amino Acid Polymers toward a Circular Carbon and Polymer Economy.

The development of chemically recyclable polymers via net-zero CO2 emission is considered one of the ideal solutions to alleviate carbon imbalance and advance a circular polymer economy. Amino acid (AA) polymers, an important class of polyamides, provide an attractive molecular platform for constructing recyclable polymer systems. However, classical synthetic methods for AA polymers typically involve CO2 emissions and suffer from slow polymerization rate, poor controllability, and difficulty in achieving high molecular weight. Herein, we develop a CO2-mediated synthetic strategy for AA polymers using carbamates as reactive intermediates. This strategy not only enables the ultrafast synthesis of N-carboxyanhydride (NCA) monomers from CO2 and amino acids within 1 min under mild conditions, but also realizes a robust carbamate initiation strategy for the ultrafast and controlled NCA polymerization to afford AA polymers in a short time with predictable molecular weights. The carbamate initiator exhibits high reactivity and superior stability, enabling the facile synthesis of 21-block copolymers and high-molecular-weight AA polymers with diversified structures. Mechanistic studies revealed a distinct "concerted nucleophilic addition and decarboxylation" polymerization pathway. Notably, the CO2 released during polymerization is simultaneously recycled for monomer and carbamate regeneration, forming a "fixation-release-reuse" closed-loop carbon cycle. The resulting AA polymer exhibited excellent processability with a high mechanical strength of 25.7 MPa, and could be efficiently depolymerized into amino acids with a recovery rate of 91.2%, demonstrating great potential as sustainable engineering plastics and biomaterials for circular polymer economies.