Mechanistically guided kinetic analysis of G3-catalyzed ROMP for the precision synthesis of cyclic olefin polymers

Abstract

Grubbs third-generation catalyst (G3) in ring-opening metathesis polymerization (ROMP) shows unique kinetic behaviors and ligand-addition enabled metathesis activity regulation, while several kinetic features have not been fully revealed. In this work, a thorough kinetic analysis of G3-catalyzed ROMP, for the first time, is carried out via method-of-moments-based numerical simulation and experiments. A generalized kinetic model considering possible metathesis reactions is developed and a stable-deviation-analysis strategy is proposed to estimate the rate coefficient for cyclic monomer propagation. Simulation results confirm that the number of active sites for propagation is independent of the G3 concentration, resulting in the zeroth-order kinetic dependence. Adding external pyridine ligand accelerates the consumption of G3 through a coordination competition, and a positive relation between external ligand concentration and the rate for reaching the steady-state condition is disclosed. The interchain metathesis reaction increases molar mass dispersity by increasing the weight-average molar mass, which can be effectively mitigated by adding a strongly coordinating external ligand. Analysis of ring-chain competition in intrachain backbiting suggests that increasing the initial concentration of reactants can enhance the selectivity for producing linear polymers. This study provides a comprehensive understanding of the mechanism-governed ROMP kinetic behaviors and aids in the precision synthesis of cyclic olefin polymers.