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

Abstract

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.

How to Design a Self‐Healing Polymer: General Concepts of Dynamic Covalent Bonds and Their Application for Intrinsic Healable Materials

“…Only recently, an interesting approach in order to address the problem of high mechanical robustness in self‐healing polymers was presented by Zechel et al The described polymer networks consist of methacrylate‐based copolymers crosslinked by hindered urea moieties and feature self‐healing properties as well as a remarkable hardness (Young's modulus of 0.34 GPa). Similar to acylhydrazones, urea bonds can form additional hydrogen bond interactions, which increase the network stability and mechanical performance.…”

Remendable polymers via reversible Diels–Alder cycloaddition of anthracene‐containing copolymers with fullerenes

“…Furthermore, frequency‐dependent measurements of both copolymers (CP1F and CP2F) were performed. Those measurements allow drawing conclusions about the formation of a network structure as well as, in the case of supramolecular systems, of the network reversibility . For this purpose, both copolymers were measured at room temperature within a frequency range from 0.1 to 100 Hz.…”

“…Furthermore, the mechanical behavior was studied using rheology measurements (Figure S8). Those investigations were already applied for self‐healing systems in order to understand the mechanical behavior during thermal treatment . This behavior was also studied for the copolymers CP1F and CP2F.…”

Self‐Healing Metallo‐Supramolecular Amphiphilic Polymer Conetworks

“…In addition to self‐healing feature, the use of metal complexes enlarges the properties and functionalities of the resulting materials, including but not limited to light responsive, solvatochromic, conductive, and highly stretchable polymers . Nevertheless, the current challenge in self‐healing materials lies in the design of materials that combine self‐healing ability and good mechanical properties . One of the strategies that has been used to overcome this limitation is the design of phase‐separated nanostructured polymers with the hard phase providing good mechanical properties while the soft one, equipped with the supramolecular bonds, endows the materials with the self‐healing behavior.…”