Stress-Sensing Thermoset Polymer Networks via Grafted Cinnamoyl Mechanophores in Epoxy

The employment of mechanophores and mechanochemistry in materials has enabled the development of novel force-responsive materials. Studies exploring the force sensing capabilities of the UV-dimerized cinnamoyl moiety have shown that after severing its cyclobutane bond under application of an external force, the moiety will revert to its initial fluorescent state. This has been experimentally demonstrated in literature through embedding the cinnamoyl group into an epoxy thermoset matrix. However, the covalent grafting of these mechanophores into the backbone of a thermoset is noticeably missing from mechanophore literature. Two specific approaches for bonding the cinnamoyl group have been explored. These include bonding the cinnamoyl group to the epoxide within the resin component, as well as a bonding to an amine-based hardener molecule. The goal of this work is to improve upon the fluorescent response of the cinnamoyl moiety as well as mitigate property loss from mechanophore incorporation over previous particulate approaches. Additionally, this work aims to provide a fundamental understanding of mechanochemistry as a whole.