Sustainable closed-loop recycling of vinylogous urethan-based covalent adaptable networks: Impact of branching nodes on mechanical strength and recyclability

The introduction of Covalent Adaptable Networks (CANs) provides a novel strategy to overcome the inherent limitations of traditional thermosetting polymers, such as difficulties in reprocessing and recycling. However, significant challenges remain in diversifying network topologies, balancing dynamic processing capabilities with network stability, and achieving efficient recycling through the repeated reuse of monomers. In this study, we synthesized multifunctional acetoacetate monomers via a thiol-ene click reaction between polyfunctional thiols and allyl acetoacetate, and subsequently constructed closed-loop recyclable CANs based on vinylogous urethane bonds by reacting these monomers with tris(2-aminoethyl)amine (TREN). The effects of different network topologies on mechanical performance, dynamic responsiveness, and thermal stability were systematically investigated. The results demonstrated that networks with higher crosslink densities exhibited enhanced mechanical strength and chemical stability. Contrary to the common notion that high crosslink density leads to higher activation energies, we increased the local concentration of dynamic bonds through an optimized branching-node design, thereby significantly lowering the activation energy required for bond exchange and further improving dynamic responsiveness. Furthermore, we optimized a mild acidolysis method enabling rapid depolymerization and efficient monomer recovery, successfully achieving closed-loop recycling and performance upgrading of the materials. This work provides new theoretical insights and technical guidance for the development of closed-loop recyclable CANs exhibiting both high dynamic processability and robust stability.