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

Various combinations of commercially available Lewis bases (1-methylimidazole, 4-(dimethylamino)pyridine, 1,4-diazabicyclo(2.2.2)octan and diazabicyclo-undecene) 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, DBU 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 DBU 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 1h.