Molecular Insights into Interfacial Stress Amplification and Network Reinforcement in Extrudable Multiphase Vitrimers

Incorporating dynamic covalent bonds (DCBs) into elastomers provides a seminal solution for the upcycling of traditional thermoset elastomers. Recently, engineering a multiphase network with various cross-linking uniformity and phase structures has been proven to be an effective strategy to overcome the bottleneck of continuous and high-throughput recycling (e.g., extrusion reprocessing) of vitrimeric elastomers. However, all of the relevant studies only focused on revealing the influences of network structures on the macroscopic properties of the systems. As for the microscopic mechanism of the multiphase network at the molecular level, it is still lacking. Herein, based on coarse-grained molecular dynamics (CGMD) simulation, a modeled DCBs-cross-linked elastomer with a multiphase network was established, which was subsequently subjected to in situ tensile or shear forces to simulate the evolution of local chain segment motion and stress/strain distributions in various microregions of the network under the complex extrusion/injection force field. The results indicate that phase domains with different cross-link densities feature distinct chain segment motion behavior and local stress/strain distribution evolution during tensile/shear deformation, and the interfacial phase exhibits significant high stresses. Therefore, incorporating heterogeneously cross-linked multiphase networks into elastomeric vitrimers can enable the system to have significant network reinforcement and unique interfacial stress amplification effects, which are critical for determining extrusion/injection reprocessability. Therefore, we envisage that the present study can provide a molecular-level theoretical explanation for the extrusion/injection reprocessability of multiphase elastomeric vitrimers, thereby guiding the rational network/performance design of these seminal materials.