Evaluation of ruthenium catalysts for ring-opening metathesis polymerization-based self-healing applications

Self-heating polymers based on ring-opening metathesis polymerization incorporate first-generation Grubbs' catalyst as the polymerization initiator during a healing event. However, the use of this catalyst imposes limitations due to the catalyst's chemical and thermal instability typically encountered in processing and curing of epoxy resins. In this work, we compare three variations of Grubbs' catalysts (first generation, second generation, and Hoveyda-Grubbs' second generation) for use in self-heating polymers. Specifically, we examine the dissolution properties, initial polymerization kinetics, chemical stabilities, and thermal stabilities for all three catalysts. Furthermore, the reactivities of the three catalysts with various monomeric healing agents are compared with a view toward improving the self-healing performances in a variety of epoxy matrices, with disparate surface properties, by promoting noncovalent interactions between the epoxy matrices and the polymerized healing agents. Due to its thermal stability and functional group tolerance, second-generation Grubbs' catalyst emerges as the most versatile catalyst especially for high-temperature applications and use with healing chemistries aimed at improving self-healing performance via noncovalent interactions.