Effect of ligand structure in the trimethylene carbonate polymerization by cationic zirconocene catalysts: A “naked model” DFT study

Abstract

DFT calculations were performed on the cationic ring-opening polymerization (CROP) reaction of trimethylene carbonate (TMC) by the “naked cation” zirconocene catalyst, [Cp2ZrMe]+. Two reaction steps of the CROP (initiation and chain propagation) are considered. Using a set of 29 catalyst structures that differ in electronic and steric properties, the effects of ligand modification on the catalyst performance are explored. The calculations support the activated chain-end mechanism of the process, providing structural, energetic and electronic properties of key cationic species involved. It is found that varying ligand structures tend to destabilize the complexation in the initiation step and lower the activity of the chain propagation. Furthermore, the stability and reactivity of CROP cannot be ascribed solely by electronic origin as steric effect between the ligand and monomer is also playing a role. The effect of solvent and dispersion on the CROP reactivity was also investigated with the results, indicating that it plays a dominant role in the initiation process. The results in this paper might contribute to further improvements of this catalytic system.