Mechanophores in self-healing polymers: Influence of mechanical bond activation on the self-healing performance of polymers

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Self-healing polymers are capable of restoring their original functionalities after being damaged. In particular, intrinsic self-healing polymers based on different reversible interactions have been investigated intensively. Besides different supramolecular interactions mainly reversible covalent interactions have been studied. Within this context reversible addition (e.g. Diels Alder reaction) as well as condensation reactions (e.g. imines, acylhydrazones) have been investigated. Much research was devoted to elucidate the healing process and the underlying healing mechanism, respectively, of different reversible polymer networks. Despite the significant knowledge gained, the damage event as well as the results of the damage (besides an obvious scratch/crack) remain uncertain. Consequently the question arises: 'Are the reversible covalent bonds really predetermined breaking points?'Within this context this project aims at the elucidation of the occurring processes in reversibly crosslinked polymers by the introduction of mechanophores. These mechanophores will be based on donor-acceptor systems, which will be incorporated into reversible covalent bonds (thiol-ene reaction, Diels Alder cycloaddition, imines). The nature of the reversible bond (open or closed) will result in a shift of the UV vis absorption allowing the monitoring of this bonds. By this manner first the damage process can be investigated, subsequently, the healing of this polymer networks can be monitored. Consequently, the nature of the damage in connection with the mechanical activation of the polymer, i.e. of the reversible bonds, will be investigated. Different damage scenarios might lead to different activation patterns within the polymer network and consequently in differences in the healing. Noteworthy, this mechanophores will also allow a detailed study of imines, which will show a healing process based on exchange reactions. Most molecular characterization techniques will not reveal much details in case of exchange reactions (in comparison to a full opening of the reversible binding units).