| Polymeric composite materials that are able to undergo self-healing through a microcapsule-based mechanism have been developed. The first successful example of this type of material was based on the ring-opening metathesis polymerization of endo-dicyclopentadiene using Grubbs' catalyst. The work herein describes improvements made to this original material. An improved technology is described which protects and delivers the catalyst within wax microspheres. This technique leads to greatly reduced required loadings of catalyst. Faster polymerizations occur when the original endo-dicyclopentadiene is replaced with exo-dicyclopentadiene. The mechanistic reason for this difference in reactivity is examined. An alternative catalyst system based on WCl6, phenylacetylene, and nonylphenol has also been developed. In addition to these microcapsule-based materials, work toward self-healing based on stress-activation of polymerization is described. As a prerequisite to developing this technology, demonstration and characterization of polymerization initiated by diradicals from cycloaromatization reactions has been performed. Polymeric materials containing cycloaromatization substrates can be stressed significantly without the observation of significant amounts of cyclization. |
