Grafted Cinnamoyl-Based Mechanophores for Self-Sensing and Photochemical Healing Capabilities in Epoxy

While understanding of failure mechanisms for polymeric composites has improved vastly over the recent decades, the ability to successfully detect and subsequently prevent early failure has consequently attracted much interest. Covalent polymer mechanochemistry, where designed chemical reactions can be initiated by deforming specific bonds present in certain moieties, is the field of chemistry that is specifically applied to realize such advanced functionalities for polymer-based materials. In this work, the cinnamoyl moiety, which is a mechanophore that is capable of undergoing cycloreversion to produce a measurable fluorescence signal, is cross-linked into the backbone of an epoxy thermoset to form a force-responsive polymer network. This approach aims to not only limit the mechanical and thermal property loss of incorporating mechanophores into polymer systems but also enhance the force sensitivity of the mechanophore itself. Additionally, a photochemical healing feasibility study was performed to take advantage of the reversible [2 + 2] cycloaddition reaction of the cinnamoyl mechanophore for epoxy photochemical healing. Ultimately, this work successfully improved the mechanical and thermal properties over neat epoxy, increased the mechanophore sensitivity from previously reported standards for the cinnamoyl moiety, and demonstrated effective photochemical healing capabilities.