Judging from the amount of research activity spawned in academia, and efforts in industry since White et al. reported the first self-healing polymeric material system,1 there is little doubt that designers of novel polymeric materials find the potential of self-healing functionality intriguing. In White’s system, microencapsulated dicyclopentadiene (DCPD) and Grubbs’ catalyst particles were embedded into a bisphenol-A/epichlorohydrin epoxy resin (EPON 828) cured with diethylenetriamine. Damage to the cured resin ruptured the microcapsules, releasing the DCPD into the site of damage, where upon contact with the catalyst, a ring opening metathesis polymerization was initiated, restoring structural continuity to the polymerized resin. With a view towards increasing compatibility with other polymer matrix materials, decreasing cost and minimizing toxicity, White and others have developed additional self-healing chemistries based on condensation and addition polymerization of silicone resins,2-4 epoxy resin chemistry,4,5 reaction of isocyanates,6 and free-radical-initiated polymerization of acrylates,7 to cite a few examples.
Although some of the academic research in the area of self-healing materials has moved on towards other approaches such as designing self-healing functionality into materials via microvascular networks or leveraging supramolecular interactions,3 microcapsules remain the most viable option where protective coatings are concerned. Unlike the use of microvascular networks or supramolecular functionality that might require the design of completely new classes of resins or fundamentally change the way coatings are designed, manufactured and applied, microcapsules can be incorporated into a coating with minimal adjustments to the batch-making process.