Self-healing Materials: Click Chemistry
Self-healing materials with ROMP healing agent system are well developed. However, the cost of ROMP system is very high. Assume that the matrix is made of epoxy, which is around $0.10/gram. The healing agent, DCPD, is a by-product of refinery, and it is $0.07/g even cheaper than epoxy matrix. The catalyst which triggers the ROMP, is really expensive, $71.80/g. Considering the composition of self-healing material, the overall cost of per gram self-healing material would be more than $1.89/g if take the processing cost in account. Does anyone want a self-healing materials cost so much? No, we need develop a brand new low-cost system with similar or better self-healing functionalities.
The azide/alkyne ‘click’ reaction is a recent re-discovery, and has many advantages: 1) high yielding; 2) reactive in ambient conditions; 3) no or benign solvents; 4) fast reaction kinetics; 5) minimal or inoffensive byproducts. All of these meets the healing agent requirements for fabricating a successful self-healing materials.
The most common Click reaction is called CuAAC, Cu-catalyzed Azide-Alkyne Cycloaddition, as shown as in the figure. Several azides and alkynes are designed and successfully synthesized. The overall cost of the CuAAC system we are working on is around $0.27/g, much cheaper than the self-healing materials based on ROMP system.