Unraveling the Heterogeneity of Epoxy-amine Networks by Introducing Dynamic Covalent Bonds.

Epoxy resins are a kind of universal thermosetting plastics, which are widely used as structural materials in various applications. Thus, it is necessary to understand the network structure of epoxy resins. However, it is challenging to reveal the network heterogeneity of epoxy resins due to the permanent covalent crosslinking. Here, we provide a novel strategy to characterize the network heterogeneity of epoxy resins by using the dynamic covalent bonds to replace the conventional covalent bonds. The dynamic covalent bonds can reorganize under heat stimulus and the network keeps a constant crosslinking density during topological rearrangement, making it convenience to study the heterogeneity of epoxy resins. Kohlrausch-Williams-Watts (KWW) stretched exponential function is used to fit the stress relaxation data, and the parameters β and σperm/σ0 extracted from KWW equation indicate the network becomes more homogenous with the stoichiometric ratio of epoxy groups and amines decreases from 1/1 to 1/1.5. This method proves that the side reaction between epoxy and hydroxyl is the main origin of the structural heterogeneity in epoxy resins compared to the secondary amines network. [ABSTRACT FROM AUTHOR]