Influence of Grubbs Catalyst Concentration on the Rheokinetics, Mechanical, and Thermomechanical Properties of Dicyclopentadiene-Based Networks

Dicyclopentadiene (DCPD) undergoes rapid ring-opening metathesis polymerization (ROMP) in the presence of Grubbs catalyst (GC), yielding a highly cross-linked thermoset polymer known for its exceptional mechanical strength, chemical resistance; high glass transition temperature (<i>T</i> _g); low dielectric constant; and superior thermal, hydrolytic, and radiation stability. This study systematically examines the effect of varying GC concentrations from 0.04 to 0.3 wt % on the curing kinetics, thermomechanical behavior, and mechanical performance of poly-DCPD networks. Rheological analysis demonstrates that increasing GC concentration significantly accelerates polymerization and gelation, effectively reducing pot life and presenting challenges for controlled processing. However, despite the variations in curing rate, the activation energy of the polymerization reaction remains essentially constant across all catalyst concentrations, indicating that GC influences the reaction kinetics by increasing the number of active catalytic sites rather than altering the intrinsic energy barrier. The curing behavior is well described by the Winter-Chambon criteria, with both storage modulus (<i>G'</i>) and loss modulus (<i>G″</i>) exhibiting power-law dependence on frequency, and their respective exponents intersecting precisely at the gel point. Dynamic mechanical analysis reveals a clear trend of increasing storage modulus and <i>T</i> _g with higher GC levels, signifying enhanced cross-link density and a more rigid polymer network. Mechanical characterization shows a near-linear increase in tensile strength as GC content rises, while elongation at break improves up to an optimal catalyst concentration (∼0.2 wt %), after which it slightly decreases due to increased network stiffness and reduced chain mobility. These results demonstrate that precise tuning of GC concentration offers a robust strategy to modulate curing kinetics and achieve an optimal balance between strength and toughness in poly-DCPD thermosets. Such control is critical for scaling up processing and improving fracture resistance in large-area coatings and composite applications where controlled cure profiles and mechanical reliability are paramount.