Polymerization of Ethylene Terephthalate Cyclic Oligomers with Antimony Trioxide

Conditions for polymerizing ethylene terephthalate cyclic oligomers (ETCs) with the catalyst antimony trioxide were investigated with the ultimate goal in mind of using ETCs to produce high-performance poly(ethylene terephthalate) (PET) composites. The ETCs used were prepared both by a direct synthesis method and by cyclodepolymerization (CDP) in dilute solution. ETCs prepared exhibited a distribution of oligomeric species displaying a broad melting range, the uppermost end of which lies at 290 °C. In the case of ETCs prepared by CDP, purified ETCs (p-ETCs) were prepared by eliminating remaining impurities including linear oligomers and cyclic oligomers containing the diethylene glycol (DEG) unit using dichloromethane and tetrahydrofuran. A homogeneous mixture of ETCs prepared by the direct synthesis method or p-ETCs with antimony trioxide was successfully polymerized to high molecular weight (MW) PET (Mn ≥ 25 000) at 293 °C within 15 min. The lower the contents of remaining impurities, the higher the MW ...