Aromatic molecules are among the most ubiquitous and structurally robust motifs in chemistry, yet their direct implementation as monomers in metathesis polymerization has long been considered unattainable due to their substantial aromatic stabilization. Overcoming this intrinsic stability without complete loss of aromaticity represents a longstanding challenge in polymer synthesis.
Here, we report the ring-opening metathesis polymerization of aromatic monomers enabled by a cascade process. The monomers are built on an indole scaffold bearing a phenyl acetylene handle that functions as a kinetic trigger. Rapid alkyne insertion initiates a selective intramolecular cascade that redistributes energy and enables aromatic ring opening with regeneration of an aromatic motif. Rather than directly disrupting aromatic stabilization, this strategy reorganizes it to enable incorporation into the polymer backbone.
Using commercially available Grubbs third-generation catalyst (G3), we achieve controlled metathesis polymerization of these aromatic monomers with high cascade efficiency. Monomers bearing both electron-donating and electron-withdrawing substituents undergo successful polymerization, demonstrating broad functional group tolerance. By systematically varying substituents on the monomer framework, we further modulate the polymerization rate by up to 15-fold, demonstrating precise kinetic control over the cascade process. Block copolymer synthesis further supports the living character of this cascade aromatic ring-opening metathesis polymerization.
Mechanistic studies based on in situ NMR monitoring and DFT calculations reveal that alkyne insertion, rather than aromatic ring opening, constitutes the rate-determining step. Intramolecular indole coordination slightly reduces aromaticity, lowering the barrier for ring opening and facilitating the cascade process under metathesis conditions. These findings demonstrate that aromatic ring opening is accessed through kinetic regulation rather than direct disruption of aromatic stabilization.
Collectively, this work establishes a general strategy for achieving aromatic ring opening in the metathesis polymerization of aromatic monomers, transforming aromatic stability from a synthetic constraint into a design element.

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