Large-Strain Viscoelasticity of Partial Vitrimer Silicone Rubber Networks with Stress-Assisted Bond Exchange and Topological Constraints

Partial vitrimer elastomers that combine static and dynamic covalent crosslinks provide a promising route to reconcile creep resistance with network reconfigurability; however, the mechanistic understanding of their cooperative roles under large deformation remains limited. Here, we report a high-performance silicone rubber system based on polymethylvinylsiloxane (PMVS) incorporating dynamic boronic ester bonds and static covalent crosslinks with tunable compositions. The resulting materials exhibit exceptional stretchability (>1200%) together with enhanced tensile strength and improved elastic recovery under large strains. Rheological and mechanical analyses reveal that dynamic covalent crosslinks (DCCs) enable topological rearrangement, leading to enhanced damping, extensibility, and rate-dependent response, while static covalent crosslinks (SCCs) provide a persistent elastic backbone and impose topological constraints that suppress long-time flow and delay DCC-mediated relaxation. To quantitatively describe this behavior, we develop a constitutive model that integrates non-Gaussian chain elasticity with finite extensibility, stress-assisted bond-exchange kinetics, and static-crosslink induced topological constraints. The model accurately reproduces rate- and strain-dependent mechanical behavior and enables direct partitioning of viscoelastic contributions from the static and dynamic subnetworks. This work establishes a quantitative constitutive framework linking effective bond exchange kinetics and hybrid network topology to the macroscopic nonlinear mechanics of partial vitrimer elastomers under large strains.