The synthesis of bottlebrush polymers by ring-opening metathesis polymerization (ROMP) of macromonomers (MMs) is controlled by the competition between the kinetics of the polymerization and the lifetime of the catalyst. Ultimately, the degree of polymerization (DP) is highly dependent on the rate of propagation versus the rate of termination, and in order to reach a target DP, a MM with a large propagation constant, kp, compared to the termination constant is desired. The anchor group–the configuration of atoms linking the polymer to a polymerizable norbornene–has been shown to affect the propagation rate of various MMs by changing the highest-occupied molecular orbital (HOMO) energy. We calculated the HOMO energy of a variety of nobornene-containing monomers with anchor group-like moieties. The kinetics of ROMP of some of these monomers and similar MMs initiated by (H2IMes)(pyr)2(Cl)2Ru=CHPh (Grubbs third generation catalyst) were evaluated and compared to the respective HOMO energies. We observed a linear trend with HOMO energies less than -150 kcal mol-1 and a weaker dependence on HOMO energy for monomers with higher HOMO energies. To further understand the effect of the anchor group, monomer chelation to the catalyst and catalyst death were also studied.

Optimization of ring-openeing metathesis polymerization for the synthesis of bottlebrush polymers

ACS Fall 2021

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