Lewis base/oxirane combinations as catalytic system in the glycolysis of poly(ethylene terephthalate) and the ring-opening polymerization of ε-caprolactone

Abstract Various combinations of commercially available Lewis bases (1-methylimidazole, 4-(dimethylamino)pyridine, 1,4-diazabicyclo[2.2.2]octan and 1,8-diazabicyclo[5.4.0]undec-7-ene) were employed alongside phenyl glycidyl ether as a co-catalyst for the polymerization and depolymerization of polyester compounds. During the glycolysis-based degradation of commercial-grade PET, it was found that only 1-methylimidazole enhances the reaction kinetics when combined with oxirane, resulting in a drastic reduction in degradation time. This phenomenon can be explained by the in situ formation of an N-heterocyclic carbene through the reaction between the azole and the oxirane. In the polymerization of ε -caprolactone, 1,8-diazabicyclo[5.4.0]undec-7-ene is the only Lewis base that yields moderate conversion (64%) under the applied conditions (90 °C, 24 h reaction time, no solvent). Adding benzyl alcohol as an initiator resulted in faster, higher conversion for diazabicyclo[5.4.0]undec-7-ene but had no effect on the other Lewis bases. When the oxirane was added as the sole co-catalyst, all Lewis bases fully polymerized the lactone within 24 h. The fastest polymerization was achieved by adding benzyl alcohol to the Lewis base/oxirane catalytic system, as complete polymerization of the lactone occurred within 1 h. Graphical abstract