Mechanically Robust Polyvalerolactone Thermosets with Dual Recyclability

Abstract

While the incorporation of dynamic covalent bonds (DCBs) in thermosets is widely employed, the materials inevitably downgrade substantially during repetitive physical recycling. Meanwhile, chemical recycling of polymers back to starting monomers often requires significant energy/resource input during the (de/re)polymerization process. To address such a dilemma, we propose a dual-recycling strategy that integrates the advantages of DCBs and chemical recycling by cross-linking chemically recyclable polyesters with DCB-containing cross-linkers. A series of poly(valerolactone) (PVL)-based covalent adaptable networks (CANs) were constructed featuring a functionalized PVL backbone and dynamic boronic-ester-containing cross-linkers to enable simultaneous physical and chemical recyclability. Through fine-tuning the balance between crystallinity and cross-linking density, the CANs exhibited outstanding mechanical properties, including a tensile strength up to 17.7 MPa and an elongation at a break of 1164%. Owing to the dynamic exchange characteristic of boronic esters, the CANs retained nearly identical performance to the original samples after five cycles of physical recycling. Furthermore, the CANs could undergo catalytically assisted chemical recycling with Sn(Oct)₂, allowing the recovery of starting monomer. This work provided a valuable approach for the development of dual-recyclable high-performance polymer networks as a potential solution to the current challenges in thermosets recycling.