Preparation of Colorless, Highly Transparent, Epoxy-Based Vitrimers by the Thiol-Epoxy Click Reaction and Evaluation of Their Shape-Memory Properties

Vitrimers are functional cross-linked materials with an associative bond-exchange mechanism. Here, we demonstrate the preparation of colorless and highly transparent epoxy-based vitrimers by using a simple reaction of commercially available, thiol-functionalized, and epoxy-functionalized monomers, that is, trimethylolpropane tris(3-mercaptopropionate) (Tri-SH) and bisphenol A diglycidyl ether (di-epoxy), which can thus contribute to the practical application of vitrimers because conventional vitrimers, especially epoxy-based vitrimers, suffered from a yellowish color and poor transparency. The present preparation includes another advantage of the efficient progress of the cross-linking reaction under relatively mild and quick reaction conditions (120 °C, 2 h) in comparison with the reported epoxy-based vitrimers, owing to the "click" nature of the thiol–epoxy reaction. Because the Tg evaluated by differential scanning calorimetry is close to room temperature, the obtained vitrimer shows a Young's modulus comparable to glassy polymers and also ductile tensile property, which is another advantage in terms of mechanical properties. Vitrimeric properties, such as the softening temperature and stress relaxation, are first evaluated, and the unique shape-memory property with a shape-editable function owing to the capability of network topology alternation is also demonstrated.