Robust, Reprocessable and Scalable Ethylene Acrylic Acid Copolymer (EAA) Derived Vitrimer Based on Dual Cross-linked Networks

Abstract

Vitrimers possess the dual advantages of thermoplastics and thermosets, combining reprocessability with excellent mechanical property, heat resistance, and solvent resistance. Ethylene acrylic acid copolymer (EAA) is a widely used semicrystalline thermoplastic that suffers from low Vicat softening point and poor creep resistance. Previously, we demonstrated a simple, efficient and scalable avenue to EAA derived vitrimer with excellent creep resistance and reprocessability. Yet the overall mechanical properties were suboptimal. In order to address this issue, dual cross-linked EAA vitrimers, namely, EAA-GDE-ZnO (GDE and ZnO represent ethylene glycol diglycidyl ether and zinc oxide, respectively), based on dynamic β-hydroxy ester covalent bonds and zinc carboxylate ionic bonds were designed and prepared through a simple and one-step reactive blending approach starting from low-cost commercial grade raw materials. The formation of covalent and ionic cross-linking networks were evidenced by torque rheometer, FTIR, and gel fraction testing. DMA tests demonstrated that clear rubbery plateaus for EAA-GDE-ZnO showed up above the melting temperature, serving as a hallmark that distinguishes vitrimer from its thermoplastic precursor. Meanwhile, EAA-GDE-ZnO exhibited excellent creep resistance even at elevated temperatures. The mechanical properties of dual cross-linked EAA-GDE-ZnO were significantly enhanced compared to its single cross-linked counterpart. Owing to the dynamic features of β-hydroxy ester and zinc carboxylate cross-linkages, the mechanical properties of EAA-GDE-ZnO were well maintained after 3 times reprocessing, proving the excellent (re)processability of EAA-GDE-ZnO.