(713e) Externally Triggered Healing of Thermoreversible Covalent Adaptable Network Via Self-Limited Hysteresis Heating

Conventional thermosets are synthesized using irreversible covalent bonds and typically are not capable of being remolded, dissolved, or recycled. Here, we explore a new class of materials, known as covalent adaptable networks (CANs), that incorporate reversible covalent linkages throughout the network backbone to facilitate controllable bond rearrangement and material reshaping. Specifically, we explore the thermomechanical properties and reaction kinetics of a thermoreversible Diels-Alder CAN, which is capable of complete reverse gelation and is thus fully recyclable and can be ?healed' upon material cracking or failure. The gel-point temperature, as determined by rheometry using the Winter-Chambon criterion, corresponds well to a gel-point conversion of 71%, as determined by FTIR, which is consistent with the Flory-Stockmayer equation. Interestingly, the material also exhibits a low frequency relaxation above the gel-point conversion, which compares well with the characteristic time-scale of bond rearrangement determined from the FTIR kinetic studies. Finally, we externally trigger the network rearrangement by embedding ferromagnetic chromium oxide nanoparticles that heat upon exposure to an alternating electromagnetic field. As this hysteresis heating mechanism is a self-limited and obtains a maximum temperature defined by the Curie temperature of chromium oxide nanoparticles, high temperature irreversible side reactions that frequently occur in these materials are reduced. This permits the material to be fractured and repaired at least ten times with no detectible change in its mechanical properties.