Storable, Dual-Component Systems for Frontal Ring-Opening Metathesis Polymerization

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. Current catalysts, however, induce premature polymerization within hours to days under ambient conditions. In this work, a thermally latent bis-N-heterocyclic carbene complex provides exceedingly robust resins, which are viable for 8 weeks. When mixed with Cu-I coreagents, precatalyst activation primes the system for rapid reactivity after thermal initiation. 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., T-g) 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 T-g values. Mechanistic analysis of a related model system demonstrated that an excess Cu reagent decreases the activation and polymerization rates.

Automated summary

Frontal ring-opening metathesis polymerization (FROMP) catalyzed by Grubbs-type Ru complexes allows for the rapid and energy-efficient synthesis of high-performance structural plastics. By using a thermally latent bis-N-heterocyclic carbene complex and Cu-I coreagents, the system can be primed for rapid reactivity after thermal initiation, leading to the formation of robust resins with enhanced stability. Additionally, controlling the Cu to Ru ratio significantly impacts the reaction velocity and temperature, as well as the glass-transition temperature of the resulting polymers.