Dynamic PET-Based Networks: A Critical Review of Reactive Strategies, Processing Windows, and Circular Applications

Abstract Poly(ethylene terephthalate) (PET) is an industrial commodity, with global production reaching ∼82 million metric tons in 2024 and a projected market value of USD 40.66 billion by 2025. Despite its ubiquity, PET circularity is hindered by thermomechanical degradation during recycling. This review addresses a significant gap by integrating chemical design, semicrystalline morphology, and industrial scalability. A comparison of recent developments reveals that while imine, disulfide, and boronic chemistries are widely researched, they fail in PET due to moisture sensitivity and thermal instability. Ester-based transesterification is established as the only mechanism intrinsically compatible with the PET backbone. A key highlight is that PET vitrimer behavior is morphology-limited rather than chemistry-limited. With crystallinity levels between 25% and 45%, exchange reactions are confined to the amorphous phase, resulting in heterogeneous stress relaxation and high activation energies. Furthermore, stress relaxation alone is an insufficient validation metric; molecular weight retention must be monitored to ensure flow originates from associative exchange rather than degradation. Regarding scalability, reactive extrusion (RE) is the primary industrial platform. Success depends on moisture management, defined as a first-order design variable to prevent hydrolysis within narrow processing windows. By balancing exchange kinetics against degradation, this work provides actionable principles for the scalable upcycling of PET into high-performance materials for a circular economy.