(698a) Photochemically and Otherwise Activated Covalent Adaptable Networks

Typical covalently-crosslinked thermosets have a permanent network structure that renders them intractable to post-fabrication manipulation—they cannot be melted, molded, nor dissolved. However, the incorporation of reversible crosslinks into a polymer network creates a novel material no longer limited by the irreversibly nature typical of most covalent bonds. Under certain conditions these covalent adaptable networks (CANs) possess the immutable characteristics of a chemical gel; however, once stimulated either via light or heat the covalent bonds become readily reversible and the network gains a transient nature characteristics of a weak physical gel.

In some cases the polymerization reaction can be driven far enough backwards that the polymer reverts to a liquid. Thus, unlike conventional chemical gels this novel class of materials can be readily and repeatedly manipulated after polymerization. This allows for the healing of fractures, the, complete reshaping of the material, the ready removal of the material, or the manipulation of particles within the material. Once the reaction is allowed to proceed forward again, the material recovers its original mechanical properties.

The stimulus required reverse the polymerization is readily varied and adapted. Typically, either light or heat is used to drive the reaction backwards. Thus any a variety of heating mechanisms, such as hysteresis heating, photothermal particle heating, or resistance heating can be employed to heat the material. Alternatively, photochemical CANs allow for both spatial and temporal control of the materials state. Ultimately, both approaches greatly extend the applications of polymer networks by allowing for the ready post polymerization manipulation of crosslinked materials.