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

自修复聚合物能够在被破坏后恢复其原有的功能。特别是，基于不同可逆相互作用的固有自愈聚合物已经得到了深入的研究。除各种超分子相互作用外，主要研究了可逆共价相互作用。在这种情况下，可逆加成反应（如Diels Alder反应）以及缩合反应（如亚胺，酰基腙）已被研究。对不同的可逆聚合物网络的愈合过程和潜在的愈合机制分别进行了大量的研究。尽管获得了重要的知识，但损坏事件以及损坏的结果（除了明显的划痕/裂缝）仍然不确定。因此，问题出现了：“可逆共价键真的是预定的断点吗？”“在此背景下，该项目旨在通过引入机械基团来阐明可逆交联聚合物中发生的过程。这些机械载体将以供体-受体系统为基础，将被纳入可逆共价键（硫醇-烯反应，Diels Alder环加成，亚胺）。可逆键的性质（打开或关闭）将导致紫外可见吸收的变化，从而可以监测该键。通过这种方式，首先可以研究损伤过程，然后可以监测这种聚合物网络的愈合。因此，将研究与聚合物机械活化（即可逆键）有关的损伤性质。不同的损伤情况可能导致聚合物网络内不同的激活模式，从而导致愈合的差异。值得注意的是，这种机械载体也将允许对亚胺进行详细的研究，这将显示基于交换反应的愈合过程。大多数分子表征技术在交换反应的情况下（与完全打开可逆结合单元相比）不会揭示太多细节。

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).