Hyperbranched Polymer Assisted Curing and Repairing of an Epoxy Coating

Imparting repairability to a thermoset coating without compromising other properties is desirable. In this work, a catalyst-free and repairable epoxy coating based on vitrimer chemistry was developed by using a mixture of bisphenol A epoxy (DER) and a hyperbranched epoxy (HBE) as matrix, and succinic anhydride (SA) as curing agent. The abundant hydroxyl groups in the HBE accelerate both the rates of curing and the dynamic transesterification. The presence of DER epoxy ensures the low viscosity of the coating, and its high epoxy value results in the formation of sufficient ester bonds after curing. When the epoxy curing system is used as coating for tin plate, the coating shows excellent hardness and adhesion properties. The scratch on the surface can be repaired at 150 degrees C without external pressure. The repaired coating well protects the metal substrate from corrosion in NaCl aqueous solution.