The mechanism of TBD-catalyzed ring-opening polymerization of cyclic esters

[GRAPHICS] Triazabicyclodecene (TBD) has recently been shown to be an effective organocatalyst for the ring-opening polymerization (ROP) of cyclic esters. Using DFT methods, we have studied possible mechanisms of this reaction. Our studies explain not only the narrow polydispersity index (PDI) observed in the ROP of six-membered ring lactones, but also the surprising failure of the ROP for the more reactive butyrolactone.