Self-healing 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-healing 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.

A materials system for autonomic healing of epoxy vinyl esters is demonstrated. The system is comprised of wax microspheres containing Grubbs' catalyst and microcapsules containing exo‐dicyclopentadiene (DCPD) embedded together in an epoxy vinyl ester matrix. Healing is triggered when damage in the form of a crack ruptures the microcapsules, causing DCPD to be released into the crack plane where it comes in contact and mixes with the catalyst microspheres initiating ring opening metathesis polymerization (ROMP). The chemical compatibility of the catalyst with the matrix is investigated and wax protection of the catalyst via microspheres of a sufficient size (34–98 μm) is shown to provide a suitable barrier for protecting the catalyst from free radicals generated in situ during the curing of the epoxy vinyl ester resin. Wax protection of the catalyst also allows uninhibited curing of the matrix to proceed at room temperature. Concentration of self‐healing components is varied with a view towards optimization of the recovery of virgin mechanical properties. Efficient self‐healing is observed with microspheres that are smaller than those used in previous polymer matrices. Significant recovery of virgin mechanical properties is observed within 2.5 min of healing time at room temperature and the mechanical properties of healed samples after 24 h of healing time match those of existing ROMP‐based self‐healing systems.

The suitability of various peroxide initiators for a radical polymerization-based self-healing system is evaluated. The initiators are compared using previously established criteria in the design of ring opening metathesis polymerizationbased self-healing systems. Benzoyl peroxide (BPO) emerges as the best performing initiator across the range of evaluation criteria. Epoxy vinyl ester resin samples prepared with microcapsules containing BPO exhibited upwards of 80% healing efficiency in preliminary tests in which a mixture of acrylic monomers and tertiary amine activator was injected into the crack plane of the sample after the initial fracture.

The stability of second generation Grubbs alkylidenes to primary amines relative to the first generation derivatives is investigated. For both Grubbs alkylidene derivatives, the tricyclohexylphosphine (PCy 3 ) ligand is displaced by n-butyl-A C H T U N G T R E N N U N G amine and diethylenetriamine. However, while displacement of PCy 3 in first generation Grubbs alkylidene derivatives results in decomposition of the catalyst, the N-heterocyclic carbene (NHC) ligand in second generation derivatives is not displaced by primary amines present in up to 100 equivalents. The result is the formation of new stable rutheniumamine complexes. These complexes are characterized and their catalytic activity is evaluated in ring-closing metathesis (RCM) and ring-opening metathesis (ROMP) reactions. While the amine complexes evaluated were minimally active in RCM reactions, the ruthenium-butylamine complex was significantly active in ROMP and exhibited an initiation rate constant that was at least an order of magnitude greater than that of the second generation Grubbs alkylidene from which it was synthesized.

Self-healing chemistry used for damage repair have not previously been demonstrated for free-radical polymerization pathways. However, this chemistry is important for addition polymers such as poly(methyl methacrylate) used in bone cement and epoxy vinyl ester used in dental resins. Self-healing biomaterials offer the potential for safer and longer lasting implants and restoratives by slowing or arresting crack damage. In the free-radical self-healing system reported here, the three components required for polymerization (free-radical peroxide initiator, tertiary amine activator, and vinyl acrylate monomers) are compartmentalized into two separate microcapsules-one containing the peroxide initiator, and the other containing both monomer and activator. Crack damage ruptures the capsules so that the three components mix and react to form a new polymer that effectively rebonds the crack and restores approximately 75% of the original fracture toughness. Optimal healing is obtained by a systematic evaluation of the effect of monomer, initiator, and activator concentration on healing performance.