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Intrinsic self-healing polymers with a high E-modulus based on dynamic reversible urea bonds

Zechel, Stefan; Geitner, Robert; Abend, Marcus; Siegmann, Michael; Enke, Marcel; Kuhl, Natascha; Klein, Moritz; Vitz, Jürgen; Gräfe, Stefanie; Dietzek, Benjamin; Schmitt, Michael; Popp, Jürgen; Schubert, Ulrich S.; Hager, Martin D.
in: NPG Asia Materials (2017) e420-1

The straightforward synthesis of a urea polymer network is presented. Commercially available monomers are polymerized using light-induced polymerization, resulting in networks crosslinked by hindered urea molecules. These moieties are reversible and, thus, can be converted into the starting compounds (that is, isocyanate and amine) by a simple thermal treatment. This process is monitored using differential scanning calorimetry as well as Raman and infrared spectroscopy. Furthermore, the self-healing ability of these polymer networks is investigated using scratch-healing tests as well as bulk-healing investigations using tensile testing. The resultant materials have a high E-modulus, are able to heal scratches at temperatures above 70 degrees C multiple times and their mechanical properties can be partially regenerated. The underlying healing mechanism is based on the reversible opening of the urea bonds and exchange reactions between two functional groups, which were confirmed from a spectroscopic analysis. In summary, these new materials are a new type of intrinsically healable polymers and provide a first step toward hard and healable polymers.

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