Ring-opening metathesis polymerization (ROMP) exhibits living characteristics under many conditions when mediated by Grubbs’ first-generation catalyst [G1, (PCy3)2(Cl)2RuCHPh] and Grubbs’ third-generation catalyst [G3, (H2IMes)(Cl)2(pyr)2RuCHPh]. However, it still has limitations. We studied how monomer choice, and specifically the anchor group, affects livingness of ROMP. We calculated the HOMO energy of 61 monomers and performed kinetic experiments to measure the propagation rate of eight monomers with different anchor groups. We observed a positive correlation between the HOMO energy and kp,obs with both catalysts and showed a 30-fold and 10-fold increase in kp,obs between the monomer with the lowest HOMO energy and the monomer with the highest HOMO energy for G1 and G3, respectively. We measured chelation for these eight monomers, and we studied the effects of monomer choice on catalyst decomposition, a key termination pathway for ROMP. Finally, we evaluated the anchor group in macromonomers containing these anchor groups to make bottlebrush polymers. Overall, we find that the best way to improve the livingness of ROMP is to enhance kp, highlighting the importance of the anchor group. Calculating the HOMO energy of monomers provides an easy method to predict propagation rates for more insightful monomer selection in the future.

Livingness in ring-opening metathesis polymerization: The effect of the anchor group

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