Covalently crosslinked polymers are generally classified as thermosets, which cannot be recycled, remended, or remolded. To develop responsive materials, dynamic bonds can be built into the network architecture, which can undergo bond rearrangements that impart desirable macroscopic properties such as the ability to relieve stress, reconfigure, reshape and heal [1, 2]. Often, these reactions are activated by an external stimulus such as light or heat. An alternative approach is to utilize mechanical deformation as a trigger via the incorporation of mechanophores, or mechanically-active groups, into the network. We have developed a new responsive material which heals after damage with enhanced local strength providing reinforcement where the material was once weakest . Our approach incorporates a sacrificial bond into a polymer strand, which homolytically cleaves under a large, non-linear deformation. The cleaving of this polymer strand results in local polymerization and a concomitant increase in local material strength, thus mitigating macroscopic fracture. The energy from the damage event itself is therefore the trigger to heal and represents an important step towards developing responsive materials that heal without human intervention.
References: Kloxin, C. J., and Bowman, C. N., â??â??Covalent adaptable networks: smart, reconfigurable and responsive network systems,â??â?? Chemical Society Reviews 42, 7161-7173 (2013).
 Kloxin, C. J., Scott, T. F., Adzima, B. J., and Bowman, C. N., â??â??Covalent Adaptable Networks (CANS): A Unique Paradigm in Cross-Linked Polymers,â??â?? Macromolecules 43, 2643-2653 (2010).
 Gordon, M. B., French, J. M., Wagner, N. J., and Kloxin, C. J., â??â??Dynamic Bonds in Covalently Crosslinked Polymer Networks for Photoactivated Strengthening and Healing,â??â?? Adv Mater 27, 8007-10 (2015).