Reaction pathway engineering enables sequence-regulated upcycling of post-consumer PET into tunable sustainable copolyesters

Reaction pathway engineering enables sequence regulation beyond composition control. • Post-consumer PET waste is converted into purified rBHET through catalyst-free glycolysis. Condensation pathways govern sequence distribution and copolyester properties. • NMR-guided sequence analysis reveals structure–property–degradation relationships. • Pathway-controlled PET upcycling produces sustainable copolyesters with tunable performance. The chemical recycling of poly(ethylene terephthalate) (PET) provides a promising route toward circular polymer production; however, controlling molecular sequence distribution during PET repolymerization remains largely unexplored. In this study, a reaction pathway engineering strategy is developed to construct sequence-tunable recycled bis(2-hydroxyethyl) terephthalate (rBHET)-based copolyesters from post-consumer PET waste. Catalyst-free glycolytic depolymerization was combined with Sb 2 O 3 -catalyzed melt polycondensation through two distinct condensation pathways: transesterification using rBHET/dimethyl furan-2,5-dicarboxylate (DMFD)/dimethyl adipate (DMA) and mixed esterification–transesterification using rBHET/DMFD/adipic acid (AA). By regulating condensation pathways and DMFD incorporation, the sequence distribution and resulting chain organization were systematically tuned. Nuclear magnetic resonance analysis revealed pathway-dependent sequence variations, with randomness parameters ranging from 0.61 to 0.96. The optimized copolyester exhibited a balanced mechanical performance with a Young’s modulus of 1487 MPa, tensile strength of 58 MPa, and elongation at break of 205%. Furthermore, sequence architecture influenced enzymatic degradation behavior by modifying chain packing and ester bond accessibility, as demonstrated by Candida antarctica lipase B (CALB)-mediated degradation. This work demonstrates reaction pathway engineering as an additional molecular design strategy for transforming PET-derived feedstocks into recycled copolyesters with tunable sequence structures and application-oriented properties.