Scaffolded Thermally Remendable Hybrid Polymer Networks

Step-growth Diels–Alder (DA) networks using furan and maleimide groups are particularly useful in forming thermally remendable crosslinked polymers, due to the dramatic shift in equilibrium over a relatively low temperature range as compared with other diene-dienophile pairs. However, the efficient healing observed in these materials at high temperature is directly tied to their ability to depolymerize and flow, and thermal treatment often results in deformation of the original shape. To overcome this limitation, a hybrid network material is developed, which consists of orthogonal Diels–Alder and polyurethane networks. Both step-growth networks form simultaneously at elevated temperature without the presence of a catalyst. At high temperatures, the Diels–Alder network depolymerizes and flows into fractures through capillary action, while the polyurethane serves as a scaffold to maintain the overall shape of the sample. The DA network then repolymerizes at lower temperatures, creating a crosslinked, scar-like “patch” throughout the crack. This healing process is repeatable without concern of monomer depletion. During heating through the glass transition, a shape memory “assist” is observed, which reverses some of the localized damage by bringing broken edges closer together. Samples are repeatedly damaged and then healed through temperature cycling, as evidenced through tensile fracture tests and electrochemical conductivity tests.