Effect of cross-link density on the performance of polyimine/epoxy vitrimers

Vitrimers are polymers rich in dynamic covalent bonds in cross-link networks. When the dynamic covalent bonds are not activated, the vitrimers show the performance stability of the traditional thermosetting polymer. When the dynamic covalent bonds are activated, the vitrimers can show some novel and unique properties, such as stress relaxation, self-healing and reprocessing. This new type of polymer has attracted wide attention because of its unique properties. As thermoset materials, the degree of cross-link and cross-link density of the materials are very important for the performance of vitrimers. In order to find out the effects of cross-link density on the properties of vitrimers, a series of dynamic polyimine/epoxy cross-link networks with different cross-link densities were designed and prepared, and their properties were characterized. The materials with higher cross-link density show higher thermal properties, mechanical properties and shape fixation ratio. However, due to the increase of cross-link density, the mobility of molecular chain and the exchange of dynamic bonds are limited, so the healing efficiency, shape recovery ratio and shape recovery rate will decrease to a certain extent. This study provides important insights into a deeper understanding of this new type of polymer.