Closed‐Loop Polymer‐to‐Polymer Upcycling of Waste Poly (Ethylene Terephthalate) into Biodegradable and Programmable Materials

Abstract Poly(ethylene terephthalate) (PET), extensively employed in bottles, film, and fiber manufacture, has generated persistent environmental contamination due to its non‐degradable nature. The resolution of this issue requires the conversion of waste PET into valuable products, often achieved through depolymerization into monomers. However, the laborious purification procedures involved in the extraction of monomers pose challenges and constraints on the complete utilization of PET. Herein, a strategy is demonstrated for the polymer‐to‐polymer upcycling of waste PET into high‐value biodegradable and programmable materials named PEXT. This process involves reversible transesterifications dependent on ester bonds, wherein commercially available X‐monomers from aliphatic diacids and diols are introduced, utilizing existing industrial equipment for complete PET utilization. PEXT features a programmable molecular structure, delivering tailored mechanical, thermal, and biodegradation performance. Notably, PEXT exhibits superior mechanical performance, with a maximal elongation at break of 3419.2 % and a toughness of 270.79 MJ m −3 . These characteristics make PEXT suitable for numerous applications, including shape‐memory materials, transparent films, and fracture‐resistant stretchable components. Significantly, PEXT allows closed‐loop recycling within specific biodegradable analogs by reprograming PET or X‐monomers. This strategy not only offers cost‐effective advantages in large‐scale upcycling of waste PET into advanced materials but also demonstrates its enormous prospect in environmental conservation.