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°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.

The healing phenomenon of metallopolymers is studied in detail and the dependency of the chosen metal salt is provided. Furthermore, a correlation between the supramolecular bond life time and the healing behavior could be revealed.

Histidine-zinc interactions are believed to play a key role in the self-healing behavior of mussel byssal threads due to their reversible character. Taking this as inspiration, the authors synthesize here histidine-rich copolymers, as well as model histidine compounds and characterize them using isothermal titration calorimetry (ITC). With this approach, the influence of two different zinc(II) salts and the role in the complex formation of the amine function of the imidazole ring are investigated in detail. The extracted metal-ligand ratios are utilized to design novel self-healing metallopolymers. For this purpose, n-lauryl methacrylate is copolymerized with the histidine monomer via reversible addition-fragmentation chain transfer polymerization. The copolymers are crosslinked using different zinc salts, and the resulting coatings are characterized with Raman spectroscopy to investigate the metal coordination behavior and with scratch healing tests to investigate the self-healing capacity. Finally, the selfhealing behavior of the different materials is correlated with the metal-ligand binding affinity measured by ITC. 2 (2.5 g, 5.52 mmol) was dissolved in 40 mL dry dichloromethane. Triethylamine (1.53 mL, 11.06 mmol) and acetic anhydride (0.52 mL, 5.52 mmol) was added dropwise. After complete conversion, which was monitored by thin layer chromatography (TLC), the solvent and the triethylamine were evaporated in vacuo. The residue was dissolved in 50 mL chloroform and washed with 0.1 m NaHCO 3 solution and afterward with deionized water. The organic layer was dried over Na 2 SO 4 . Finally, the crude product was purified by silica gel chromatography (MeOH/CHCl 3 1:9, R f = 0.5).Yield: 2.0 g (4.04 mmol) of a white solid, 73%. Melting point: 76-77 °C. 1 H NMR (300 MHz, CDCl 3 ): δ = 0.85-0.89 (t, 3H, CH 3 ), 1.22-1.46 (m, 4H, CH 2 CH 2 CH 3 ), 1.93-2.04 (m, 4H, CH 3 Macromol. Chem. Phys. , , 1600458 M. Enke et al.

Histidine-metal interactions are utilized in many biological materials as reinforcing crosslinks, and in particular, are believed to contribute as reversible crosslinks to the intrinsic self-recovery behavior of mussel byssal threads. In this contribution, two new histidine-based monomers were synthesized and further copolymerized with butyl methacrylate (BMA) and lauryl methacrylate (LMA) applying the reversible addition–fragmentation chain transfer (RAFT) polymerization technique. Crosslinking with zinc ions resulted in supramolecular metallopolymer networks exhibiting a self-healing behavior that was tunable depending on the specific zinc salt used. The presented results provide a class of new polymeric species with different self-healing capacities

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