Two new single-component, highly cross-linked polymeric materials have been developed that are capable of undergoing repeated cycles of mending. On the basis of the thermally reversible Diels-Alder (r-DA) cycloaddition reaction, these materials are comprised of a dicyclopentadiene core which acts as both diene and dienophile in the r-DA reaction. Polymer specimens have been prepared from two monomeric units, monomers 400 and 401, and the thermal and mechanical properties of these materials have been studied via differential scanning calorimetry, dynamic mechanical analysis, and three-point bending, compression, and fracture tests. After fracture, these hard, colorless, transparent materials are capable of thermal mending at 120°C, effectively healing cracks formed in the specimen.

Mendomers are a group of polymers that are mendable upon heating. Specifically, cracks in these polymers have been shown to heal themselves when heated close to the glass transition temperature. The main mechanism behind the healing is the thermally reversible Diels—Alder reaction, where a dicyclopentadiene unit in the polymer backbone breaks apart into two cyclopentadiene terminal groups, which then reunite upon heating. The present study investigates the feasibility of using a mendomer as a matrix for re-mending composites reinforced with graphite fibers. The graphite fibers are used as electrical conductors to provide the necessary heat to the polymer. Specimens were prepared by spreading a monomer, called mendomer, powder on a graphite/epoxy laminate substrate and curing in a vacuum oven. Microcracks were introduced by bending the substrate coupon, and the latter was heated by applying electric currents. The healing behavior was confirmed by disappearance of microcracks that were observed with an optical microscope and a scanning electron microscope (SEM).