A molecular dynamics simulation on tunable and self-healing epoxy-polyimine network based on imine bond exchange reactions

In this work, a post-crosslinking method is used to construct crosslinked epoxy-polyimine networks (C-PIs) based on the imine bond. Due to the dynamic nature of the imine bond, bond exchange reactions (BERs) and rearrangements would take place in polyimine segments under heat or water external stimuli. Molecular dynamic (MD) simulations are performed to investigate imine polycondensation and post-crosslinking procedures. The results indicate that C-PIs exhibit different glass transition temperatures (Tgs) and crosslinking densities by tuning the ratio of epoxy and imine groups, and the Tg values of C-PIs increase linearly with the crosslinking density. In addition, the interface welding behaviour of different C-PIs is investigated, and our results show that BERs can improve the diffusion rate and the final penetration depth. By tracking the microstructures and examining the mechanical properties of samples varying with healing time, it is revealed that the C-PI with lower crosslinking density is easy to self-heal. Furthermore, MD results also imply that the internal stress of the C-PI can be eliminated under the coupling effect of chain relaxation and BERs. This study proves the reliability of a new crosslinking method and provides some useful guidance for designing new materials.