Transient mechanochromism in epoxy vitrimer composites containing aromatic disulfide crosslinks

4-Aminophenyl disulfide (4-AFD) has been recently reported as a hardener for the design of reprocessable, repairable and recyclable epoxy networks. Now we show that such a hardener is also responsible for a mechanochromic effect, due to an intermediate radical species formed upon damage, as confirmed by theoretical studies.