Adjusting the dynamic and mechanochromic properties of aromatic disulfide epoxy vitrimers by unsaturation of epoxy monomers

Disulfide-contained vitrimers that possess unprecedented functions, such as reprocessing and self-healing, are considered to be one of the most promising materials since they also exhibit mechanochromic behaviors. A few reports have given the phenomenon of mechanochromism, but the relationship between their structure and mechanochromic behavior needed to further research. Herein, three aromatic disulfide-contained epoxy vitrimers with different degree of unsaturation are prepared by changing the epoxy monomer. The effect of network structure on the dynamic and mechanochromic properties are investigated. With increasing the degree of unsaturation from the aliphatic to aromatic epoxy vitrimers, the T g -value increases and the chain mobility decreases, so the aliphatic epoxy vitrimers shows the lowest activation energy, the lowest temperature of malleability T v , and the shortest relaxation times. In addition, these epoxy vitrimers all showes reversible mechanochromic behaviors due to the generation and coupling of sulfenyl radicals, which can be accelerated by the high temperature and solvent. Meanwhile, the epoxy structure has a great influence on the mechanochromic behavior, including the absorption wavelength and fading kinetics of grinding powders. These results can be utilized to design desired vitrimer materials for various applications that requires both the intrinsically self-report damage and the dynamic properties such as recycling.