Vanillin-based dual dynamic epoxy building block: a promising accelerator for disulfide vitrimers

Abstract

Epoxies are one of the most versatile thermoset materials owing to their outstanding physical and chemical properties. In recent years, there have been concerted efforts to enhance the sustainability and durability of epoxy materials across a wide range of industrial applications. In this regard, vitrimers, a class of polymeric materials combining the advantages of thermosets and the recyclability of thermoplastics, have attracted significant attention. The combination of two or more covalent or non-covalent dynamic chemistries holds great promise for introducing accelerated yet tailored dynamic exchanges. Therein, a dual-dynamic bio-based epoxy building block containing both imine and disulfide bonds (DDBB), synthesized from cystamine and vanillin, has been compared to its imine-containing single dynamic analogue (SDBB). A substantial acceleration of dynamic exchanges (reflected by a decrease of the relaxation time from 4 min to 3 s at 160 °C) was revealed owing to simultaneous exchanges of imine and disulfide moieties. Building upon this, this dual-dynamic epoxy building block was introduced as a doping agent in disulfide vitrimer formulations to accelerate the dynamic bond exchanges. The results demonstrated a remarkable enhancement in exchange rates, with the relaxation time at 190 °C decreasing to as low as 21 s (with 30 w/w% of DDBB), as opposed to 25 min for the undoped counterpart. This enhancement was accomplished with minimal impact on the glass transition temperature and without substantial alteration of the curing behaviour.