Thermal analysis of ring-opening metathesis polymerized healing agents

Dicyclopentadiene (DCPD) and 5-ethylidene-2-norbornene (ENB) and their mixtures were analyzed after ring-opening metathesis polymerization (ROMP) in the presence of Grubbs catalyst as potential candidate healing agents for self-healing composite materials using two complementary methods, rotational dynamic mechanical analysis (DMA) and differential scanning calorimetry (DSC). Following isothermal DMA measurements at room temperature (RT = 25 degrees C) for 120 min, two consecutive dynamic temperature scan experiments were performed for each system. In the first dynamic temperature scans, there was an initial downward peak slightly above RT in the storage modulus versus temperature curve for samples with relatively slower reaction rates (i.e., DCPD and DCPD-rich mixtures or low catalyst loadings) due to a combination of the glass transition followed by further residual reaction. However, no or negligible downward peaks were observed for the highly reactive ENB and ENB-rich samples even at much lower catalyst loadings. Implications of the substantial decrease in storage modulus just above RT for the slowly reacting systems are discussed for healing of damage in composite materials at elevated temperatures. The maximum glass transition temperatures (T-g infinity) from DMA of the fully cured samples were determined to be approximately 160 degrees C for DCPD and 120 degrees C for ENB, decreasing linearly with increased ENB in the blends. The glass transitions and further residual reactions above the glass transitions were confirmed by DSC. (c) 2007 Wiley Periodicals, Inc.