Closed-loop recycling of semi-aromatic polyesters upcycled from poly(ethylene terephthalate)

Plastics are critical in facilitating the comfort and quality of everyday life. Most plastics are discarded after a single use, wasting the energy and carbon consumed for their production and incurring environmental costs. Thus, closed-loop production and recycling processes are needed to mitigate energy and carbon loss toward a net-zero carbon economy. Here, we show that poly(ethylene terephthalate) (PET) can be efficiently deconstructed into small-molecule α,ω-dialkenenyl terephthalates using organocatalyzed transesterification. The resulting compounds can be polymerized by acyclic diene metathesis (ADMET) polymerization, affording unsaturated semi-aromatic polyesters with thermomechanical properties dependent on the monomer structure and the catalyst used for their synthesis. High-molecular-weight ADMET polymers form free-standing films that are ductile and tough with mechanical properties similar to widely used commodity plastics. Crucially, the ADMET polymers can be deconstructed to monomers using Retro-ADMET and re-polymerized by ADMET polymerization, establishing closed-loop circularity for a unique class of materials.