A Catalyst-Free Epoxy Vitrimer System Based on Multifunctional Hyperbranched Polymer

To date, all epoxy vitrimer systems reported in the literature rely on addition of significant amounts of catalysts to achieve the dynamic transesterification reaction (TER). However, the catalysts used in vitrimers are often toxic and have poor miscibility with organic compounds, and they may further comprise the application performance like corrosion resistance. Moreover, the reprocessing and recycling properties are highly dependent on the loading amount and the type of catalyst. In this study, two hyperbranched epoxy (HBE) prepolymers are synthesized and then reacted with succinic anhydride to prepare a catalyst-free epoxy vitrimer system. It is demonstrated that both the curing during the preparation of the cross-linked materials and the TER in the resulting cross-linked materials proceed properly without addition of external catalyst. We attributed this phenomenon to the abundant free hydroxyl groups in HBE which serve as both reacting moiety and catalyst in both curing and the TER processes. At elevated temperatures (>120 °C), the TER is activated to enable fast stress relaxation of the cross-linked network. In addition, the epoxy vitrimers exhibit glass transition temperatures (T_g’s) in the range 70–96 °C, excellent thermostability, and mechanical properties similar to those of the traditional epoxy materials. By taking advantages of these features, we also demonstrate a promising self-healable and catalyst-free coating.