Unexpected efficiency of cyclic amidine catalysts in depolymerizing poly(ethylene terephthalate)

This article describes studies on the catalytic activity of several nitrogen-based organic catalysts for the depolymerization of poly(ethylene terephthalate) (PET), in which a few cyclic amidines work more effectively than a potent, bifunctional guanidine-based catalyst 1,5,7-triazabicyclo-[4,4,0]-dec- 5-ene (TBD) in the presence of short chain diols that play a role in activation of carbonyl groups through hydrogen bonding. Further studies prove that the catalytic efficiency at the above specific conditions depends only on the extent of activation of a hydroxyl group rather than simply the pKa of the bases. For glycolysis with excess short-chain alkanediols, 1,8-diazabicyclo[5.4. 0]undec-7-ene is the best catalyst. In contrast, TBD shows outstanding catalytic activity in depolymerizations of PET with mono-alcohols and longer-chain diols. Copyright © 2013 Wiley Periodicals, Inc.