Kinetic and mechanism investigation of the zwitterionic ring-opening polymerization of trimethylene carbonate catalyzed by 1,5,7-triazabicyclo[4.4.0]dec-5-ene

Zwitterionic ring-opening polymerization (ZROP) is widely used synthetic methods for cyclic polymer synthesis. While various ZROP studies utilizing organic base catalysts have been explored, reports involving 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) are rare, leaving the specific ZROP mechanism unclear. In this study, we investigate the polymerization mechanism using TBD and trimethylene carbonate (TMC). Polymerization kinetics studies reveal an irreversible formation of initiation species at the initiation reaction, showing deviation from known ZROP mechanisms using N -heterocyclic carbene as organic base catalysts. Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF-MS) results indicate that polymerization attempts using polar solvents like THF stabilize active zwitterionic species and prevent side reactions. Based on our kinetics study and MALDI-TOF-MS results, we propose the zwitterionic TMC polymerization mechanism, containing the irreversible initiation reaction.