Spatiotemporal Visualization of Intrinsic Dynamic Reversible Transesterification in Epoxy Vitrimers

Abstract

The reprocessability of vitrimers is critically governed by exchange reactivity of their intrinsic dynamic covalent bonds. However, traditional measurement techniques for vitrimers have been limited by insufficient sensitivity and low efficiency, preventing the direct detection of transesterification reactions in the solid state of polymers. In this work, we developed a highly sensitive method to visualize the transformation reaction in epoxy vitrimers by introducing fluorescent probes into the polymer network. The formation of vicinal diol structures during β-hydroxy ester metathesis was monitored in situ by coupling with boronic acid-based fluorescent probes in three-dimension via confocal laser scanning microscopy (CLSM). The fluorescent spots expanded clearly in both volume and depth with prolonged thermal treatment, revealing that the reaction between β-hydroxy ester units was highly dependent on both temperature and time. Furthermore, this study establishes a correlative relationship between the macroscopic rheological decay of epoxy vitrimers and the topological evolution of their microscopic dynamic networks under thermal treatment, providing direct visualization evidence that supports the metathesis mechanism underlying malleability degradation. This approach provides a useful tool for advancing the practical application of vitrimers in plastic waste reduction and deepens the understanding of vitrimer aging behaviors.