Frontal ring-opening metathesis polymerization (FROMP) catalyzed by Grubbs-type Ru complexes enables new, rapid, and energy-efficient syntheses of high-performance, structural plastics. Ideal catalysts survive the extended time periods associated with resin preparation, storage, and transportation. A thermally latent bis-N-heterocyclic carbene (NHC) complex provides exceedingly robust resins, which are viable for 8 weeks. When mixed with CuI co-reagents, precatalyst activation primes the system for rapid reactivity after thermal initiation via NHC transmetalation. In this study, more than 40 dual-component formulations successfully catalyzed FROMP of dicyclopentadiene. The polymerization process parameters (front temperatures and velocities), resin storability, and resultant polymer properties (e.g., Tg) were determined for each composition. Intriguingly, the Cu to Ru ratio dramatically impacts the observed frontal velocity and temperature, as well as the polymer glass-transition temperature; slower, colder reaction fronts result from formulations with large Cu to Ru ratios. The resultant polymers display lower Tg values. Mechanistic analysis of a related model system demonstrated that excess Cu reagent depresses the activation and polymerization rates.

Bis-N-heterocyclic complexes as dual-component catalysts for frontal ring-opening metathesis polymerization

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