Bio-based Tetrafunctional Epoxy Monomer Containing a Dicyclo Diacetal Structure and Its Medium-Temperature-Cured Epoxy Vitrimer System with Excellent Mechanical and Multifunctional Properties

Abstract

A bio-based tetrafunctional epoxy monomer containing a dicyclo diacetal linkage was successfully synthesized via acetalization of protocatechualdehyde (PCA) with erythritol, followed by a reaction with bioderived epichlorohydrin. The epoxy monomer exhibits good reactivity with glutaric anhydride in the presence of a zinc(II) acetylacetonate (ZAA) catalyst and can be cured using a medium-temperature procedure. The prepared epoxy vitrimer (DGZ) systems exhibit excellent mechanical and thermal properties resulting from the rigid dicyclo diacetal and aromatic structures and the high conversion of epoxy groups (αepoxy group). When the ZAA content is 2.5%, DGZ has optimal integrated mechanical properties, and its impact strength, tensile strength, and flexural strength can reach 20 kJ/m2, 60 MPa, and 119 MPa, respectively, which can be compared with those of the commercial bisphenol A epoxy resin cured with a high-temperature procedure. DGZ systems have a good glass-transition temperature (Tg) of 111–117 °C. The broad glass transition endows DGZ with a good shape memory effect. The introduction of dynamic ester bonds in DGZ brings good self-healing ability, welding ability, and rapid stress relaxation. The self-healing efficiency of the scratches on the surface of DGZ can reach ∼100% at 200 °C. Owing to the existence of dicyclo diacetal linkages, DGZ can be completely degraded in 0.1 and 1 M HCl solutions at 25–80 °C. DGZ also has good dielectric properties due to the rigid dicyclo diacetal and aromatic structures, as well as a high αepoxy group.