Diels-Alder Reaction Kinetics for the Development of Remendable Polymer Composites

Materials that can repair cracks and recover from mechanical failure are desirable. Because remendable materials both repair and prevent the propagation of cracks on the micro scale, they offer the potential for increased durability, safety, and cost efficiency for many applications. We report on the development of three healing systems for epoxy-amine thermosets based on the thermoreversible Diels-Alder reaction of furan and maleimide. In one, crack healing of a traditional epoxy-amine thermoset is induced by thermally reversible crosslinking of a secondary phase. In another, a furan-functionalized epoxy-amine thermoset can be healed with a bismaleimide solution. Both phenomena occur at room temperature and minimal pressure and significant load recovery is possible multiple times in a given location. The third system allows for interfacial healing of glass fiber-reinforced epoxy-amine composites via compatible functionalization of glass fibers and the polymer network.

Although the Diels-Alder reaction was discovered almost 70 years ago, there has not been an exhaustive study of reaction kinetics and thermodynamic parameters for furan and maleimide. We report reaction kinetic values and equilibrium concentration values for a number of model compound systems. Future work will include reactive polymer systems and relating mechanical properties to the Diels-Alder reaction. Such studies are necessary to optimize the healing ability of Diels-Alder-based systems.