Molecular Dynamics Simulation of the Structural, Mechanical, and Reprocessing Properties of Vitrimers Based on a Dynamic Covalent Polymer Network

Recyclability and reprocessability of permanently cross-linked polymeric materials have received considerable scientific and technological attention in view of the environmental pollution and sustainable development. By introducing dynamic covalent bonds, vitrimers are emerging as a promising attempt to address this pressing challenge. However, there is still a lack of thermodynamic and kinetic understanding of the bond exchange reactions (BERs) of vitrimers at the molecular level. Herein, by employing coarse-grained molecular dynamics simulations, we successfully construct a model vitrimer system composed of a polymer network formed from linear chains, which can rearrange the network topology via BERs. In this study, we examine the effect of the bond swap energy barrier (Delta E-sw) on a variety of mechanical properties. We find that Delta E-sw critically controls the dynamics of the linear chains and the reactive beads located on the linear chain. Our results indicate that the best mechanical performance characteristics are achieved at an intermediate value of Delta E-sw. Meanwhile, stress relaxations are examined for different Delta E-sw systems. By performing a triaxial deformation to induce the cavities, the vitrimer exhibits excellent self-healing capability by decreasing Delta E-sw, as well as increasing the self-healing time and temperature. Lastly, extrusion of polymer vitrimer is simulated, and we find that the extrusion rate tends to increase linearly as Delta E-sw decreases. In general, our results provide rational guidelines for designing high-performance vitrimers with good mechanical properties, excellent self-healing ability, and good reprocessability.

Automated summary

This study utilizes coarse-grained molecular dynamics simulations to investigate the effect of bond swap energy barrier (Delta E-sw) on the mechanical properties of vitrimers. The results show that Delta E-sw plays a critical role in the dynamics of linear chains and reactive beads. The study also demonstrates that an intermediate value of Delta E-sw can achieve the best mechanical performance characteristics. Additionally, the study explores the impact of Delta E-sw on stress relaxation, self-healing capability, and extrusion rate of polymer vitrimers.