Intrinsic self-healing polymers with a high E-modulus based on dynamic reversible urea bonds
One of the hardest self-healing polymers ever reported has been prepared using the reversible bonds of sterically hindered urea groups. Polymers that can re-form internal chemical links after being scratched or cracked are usually subject to design constraints that lower their mechanical strength. To overcome these constraints, Martin D. Hager and colleagues from Friedrich Schiller University Jena, Germany, created a series of poly(methacrylate) polymers bearing reversible urea units. By simply exposing the starting reagents to brief flashes of light, they prepared a cross-linked polymer featuring the urea units on the poly(methacrylate) chains resulting in mechanically tough materials. After optimizing the cross-link density, the team deliberately scratched the polymer and then heated it to begin the self-healing process. Temperatures of about 100 degree Celsius were sufficient to open urea bonds up and initiate material repair.