Investigating the Multistep Polymerization Reactions of DCPD with Grubbs’ First-Generation Catalyst

Self-healing polymer composites using Grubbs’ first-generation (G1) catalyst and dicyclopentadiene (DCPD) as the healing monomer are widely used in self-healing applications. In such systems, DCPD released from ruptured microcapsules reacts with dispersed G1, enabling healing without external intervention. This study simulates the local DCPD-G1 interaction at the crack site using Differential Scanning Calorimetry (DSC) analysis, imitating self-healing conditions. The polymerization reactions of the DCPD-G1 system were systematically investigated using DSC, Dynamic Mechanical Analysis (DMA), kinetic modeling, Fourier Transform Infrared (FT-IR), and nuclear magnetic resonance (1H NMR) spectroscopy. One of the main outcomes of this work is the identification of three separate exothermic transitions in the DSC analysis. These results indicate that the polymerization follows a multistep pathway, starting with ROMP to form linear polydicyclopentadiene (L-PDCPD) and proceeding with cross-linking via olefin addition and metathesis reactions. DMA analysis, performed within temperature intervals identified in deconvoluted DSC peaks, further clarifies that the first process involves linear polymerization, while the second and third processes are associated with cross-linking reactions. A slight increase in glass transition temperature (Tg) and shear storage modulus (G′) in the first-process interval indicates linear PDCPD growth via increased molecular weight (Mw) and chain entanglements. In contrast, a sharp increase in Tg and G′ in the sample that passed through the second-process interval and a distinct stiffness increase at the onset of the third process (∼82 °C) indicate two distinct curing mechanisms. These findings are further supported by FT-IR analysis through the monitoring of the peaks at 972, 726, and 754 cm-1. Kinetic modeling (Šesták-Berggren) closely matches experimental data, validating this multistep polymerization reaction. The findings can clearly show the multistep polymerization process for G1 - catalyzed DCPD.