Mechanism of ring‐opening polymerization of l‐lactide by lanthanide aryloxide: A theoretical study on the effect of the aryloxide ligands on the process

Abstract

AbstractA detailed mechanistic study of ring‐opening polymerization (ROP) of l‐lactide by a lanthanum aryloxide complex, La(OTMP)3 (−OTMP = 2,4,6‐trimethylphenolate), is carried out using DFT theoretical calculations. Both initiation and propagation steps were considered. The calculations reveal the two‐step coordination‐insertion mechanism, proceeding via an unprecedented lanthanum π‐arene intermediate, with the selective acyl‐oxygen bond scission of the monomer. The first step of phenolate insertion into the La − O bond of the initiator is rate‐limiting, and the bulkiness of the aryloxide ligand initiates the ROP slowly with the activation energy of 19.3 kcal mol−1, in consistent with the activation energy (15 kcal mol−1) obtained with previous kinetic experiment. Furthermore, a rationale for the broadening of molecular weight distribution reported in this initiating system is also provided.