Topology-Dependent Stress Relaxation in Epoxy Vitrimers via Reactive Coarse-Grained Modeling

Bond-exchange reactions (BERs) enable vitrimers to relax stress through dynamic topology rearrangement, yet their mechanical effectiveness depends strongly on network architecture. Here, experimental stress-relaxation measurements are combined with reactive coarse-grained molecular dynamics simulations of epoxy–acid networks with systematically varied backbone flexibility and cross-linker length. A dimensionless acceleration factor reveals consistent chemistry-dependent trends between experiment and simulation, with BER producing stronger relative acceleration in the relatively rigid DGEBA-based networks than in the flexible BDDE-based networks. Two-mode Kohlrausch–Williams–Watts (KWW) analysis separates a fast relaxation mode associated with local segmental dynamics from a slow network-level mode strongly accelerated by BER. In DGEBA-based networks, the slow stress-relaxation and topology-relaxation time scales closely correspond, indicating strong coupling between topology reshuffling and long-time stress dissipation. In contrast, BDDE-based networks exhibit substantial stress relaxation before complete topology decorrelation, consistent with their greater intrinsic internal mobility and an additional mobility-assisted relaxation pathway. These results demonstrate that the mechanical effectiveness of BER is governed not by topology-reshuffling speed alone, but by its coupling with backbone mobility and the stress-bearing network architecture.