Chemoselective Coordination-Insertion Polymerization of Cyclic Carbamates to Circular Polyurethanes with Diverse...

The synthesis of conventional step-growth condensation polymers by chain-growth ring-opening polymerization (ROP) of heterocyclic monomers holds advantages in its precise structural control and direct closed-loop circularity, but its application in polyurethane (PU) synthesis by existing cationic or anionic ROP of cyclic carbamates (CCs) presents challenges due to the limited monomer scope and low polymer molar mass or the lack of chemoselectivity. Herein, we introduce a metal-catalyzed coordination-insertion ROP (CI-ROP) of CCs that overcomes these challenges and enables controlled and chemoselective synthesis of PUs with defined architectures, including linear, cyclic, copolymeric, and cross-linked structures, accessible from a single monomer. Through coupling of monomer design and catalyst selection, this CI-ROP strategy tolerates the amide proton and bulky substituents in CCs, affords precise control over polymer microstructure and topology, and delivers PUs with molar mass up to ∼260 kg/mol. Mechanistic investigations clarify the origin of chemoselective C-O versus C-N bond cleavage under coordination (vs anionic) ROP conditions, providing a molecular-level understanding of the observed polymer architectures. Catalytic bulk depolymerization of linear and cyclic PUs recovers CCs in >90% isolated yield, while recycling of cross-linked PUs via a two-step process also recovers CCs in ∼80% yield, thanks to dynamic bond exchange that enables reversible interconversion between copolymeric linear and cross-linked PUs.