Using epoxy/acid stoichiometry to rationally tune the thermomechanical and reprocessing properties of epoxy vitrimers

Abstract

Abstract Epoxy vitrimers immerged as an appealing alternative to traditional plastics. However, high loading of catalyst and harsh processing conditions are prerequisites to fully exploit the vitrimer properties. In this work, stoichiometric ratio, an often neglected factor, was utilized to further accelerate the rate of dynamic transesterification. Epoxy vitrimers with four epoxy/acid stoichiometries (60:30, 40:30, 30:30, and 24:30) were prepared to comparatively analyze their network structures, thermomechanical properties, and reprocessing properties. It was found that the off‐stoichiometry epoxy vitrimers have almost the similar excellent thermal stability as epoxy thermosets. Vitrimers with excess epoxy showed increased tensile strength (from 26.3 to 42.7 MPa) and decreased elongation at the break (from 5.5% to 1.7%). Meanwhile, excess epoxy induced abundant of hydroxy groups in the vitrimers, imparting satisfactory repairability, reformability, and recyclability. Specifically, epoxy/acid (60:30) repaired 94% in 10 min at 180°C, and maintained over 93% mechanical properties after reforming and recycling. However, simply increasing the epoxy content will compromise the structural integrity of the network, simultaneously resulting in reduced toughness of epoxy vitrimers. These findings demonstrated that epoxy/acid stoichiometry can be a powerful tool to develop epoxy vitrimers with both excellent thermomechanical and reprocessing properties.