Polyester Oligomer is a low molecular weight compound formed as an intermediate or by-product during the production of polyethylene terephthalate (PET) and other polyester resins. It is generally composed of short chain units of terephthalic acid and ethylene glycol, appearing as a white to off-white crystalline solid or powder. Polyester oligomers play a significant role in the recycling and repolymerization process, where they are used as a raw material to produce high-grade PET resins, coatings, and adhesives. They are also widely applied in polyurethane coatings, powder coatings, and specialty adhesive formulations due to their excellent chemical reactivity and compatibility. While considered an impurity when present in excess within polyester fibers and films, controlled recovery and utilization of polyester oligomer has become increasingly important for sustainable production and circular economy practices.