Chemical control of the aromatic disulfide exchange kinetics for tailor-made epoxy vitrimers

Aromatic disulfides containing epoxy vitrimers are one of the most versatile materials and the top candidates for employment in industrial applications, as they offer many advantages compared to other existing vitrimers (scalability, simplicity, easy processing and excellent mechanical properties) and their use in industrial applications is straight forward. The capability of tuning the mechanical and dynamic properties of vitrimers is one of the most explored fields in vitrimer materials. Herein we present tailor-made aromatic disulfide containing epoxy vitrimers trough the understanding of the effect of having: i) different hardener structure (Ortho or Para); ii) free pending amine groups or; iii) catalyst in the system. Our study shows that the relaxation time is highly dependent on regioisomerism of the aromatic hardener, stoichiometry and presence of catalyst. In the present study we found that equivalent Ortho and Para vitrimers show huge difference in the activation energy (Ea) ranging from 200 kJ/mol for Para vitrimers up to 350 kJ/mol for Ortho vitrimers. In the absence of free pending amine groups, the exchange kinetics are slowed down limiting their use for continuous processing techniques. In contrast, both free pending amine groups and imidazole catalyst permit to reduce the stress relaxation time ending up in relaxation times below 5 s at 180 °C. These results confirm the high tuning capability of aromatic disulfide containing epoxy vitrimers providing a methodology to tune the dynamic properties to design the right vitrimer for the right application and processing technology.