Dynamic by Design: Unlocking Full Relaxation in Disulfide Epoxy Networks

Abstract

Aromatic disulfide-containing epoxy networks offer a promising approach to achieving sustainable materials due to their reparable, recyclable, and reprocessable properties. However, in all cases, an excess of hardener is required to achieve full reparability. In this study, a theoretical analysis demonstrates that when aromatic disulfide is incorporated into the amine hardener, the resulting epoxy vitrimer does not fully relax due to epoxy group homopolymerization, which leads to the formation of non-dynamic crosslinks. To overcome this limitation, an epoxy monomer containing disulfide bonds was synthesized. This monomer enables complete relaxation, as the homopolymerized epoxy system also contributes to the formation of dynamic crosslinks. Using this new monomer, epoxy vitrimers were prepared that can relax without requiring an excess of amine. However, these materials exhibit inferior properties compared to those prepared with an aromatic disulfide-based diamine. To enhance their properties, a non-dynamic epoxy was introduced into the formulation. Both experimental and computational results demonstrate that up to 32% of non-dynamic epoxy can be incorporated without compromising dynamic features such as repairability, reprocessability, and recyclability, making this system significantly more suitable for industrial implementation.