Reversible Crosslinking of Commodity Polymers via Photocontrolled Metal–Ligand Coordination for High‐Performance and Recyclable Thermoset Plastics

Thermoset plastics, highly desired for their stability, durability, and chemical resistance, are currently consumed in over 60 million tons annually across the globe, but they are difficult to recycle due to their crosslinked structures. The development of recyclable thermoset plastics is an important but challenging task. In this work, recyclable thermoset plastics are prepared by crosslinking a commodity polymer, polyacrylonitrile (PAN), with a small percentage of a Ru complex via nitrile-Ru coordination. PAN is obtained from industry and the Ru complex is synthesized in one step, which enables the production of recyclable thermoset plastics in an efficient way. In addition, the thermoset plastics exhibit impressive mechanical performance, boasting a Young's modulus of 6.3 GPa and a tensile strength of 109.8 MPa. Moreover, they can be de-crosslinked when exposed to both light and a solvent and can then be re-crosslinked upon heating. This reversible crosslinking mechanism enables the recycling of thermosets from a mixture of plastic waste. The preparation of recyclable thermosets from other commodity polymers such as poly(styrene-coacrylonitrile) (SAN) resins and polymer composites through reversible crosslinking is also demonstrated. This study shows that reversible crosslinking via metal-ligand coordination is a new strategy for designing recyclable thermosets using commodity polymers.