Probing the Relationship between Solvent Quality and Nonlinear Rheology in Dynamic Covalent Polymer Networks

Dynamic covalent hydrogels are hydrophilic polymer networks crosslinked by reversible bonds, enabling rapid self-healing, stress relaxation, and tunable stiffness. Designing application-specific, injectable dynamic covalent polymer networks for biomedical and therapeutic devices requires a clear understanding of their nonlinear rheological behavior, which remains poorly understood. Here, we employ coarse-grained molecular dynamics simulations with a generic bead-spring model to investigate the nonlinear rheology of 4-arm star polymers under varying solvent qualities. Our simulations reveal an increase in viscosity with improved solvent quality, which coincides with a decrease in dynamic covalent crosslink density, indicating that polymer–solvent rather than polymer–polymer interactions govern the response. Two molecular mechanisms are proposed for this solvent-mediated increase in viscosity: (1) polymer chain bridging via solvent molecules and (2) solvent migration driven by bound solvent on polymer chains. Diffusivity and nearest-neighbor analyses support the latter hypothesis as the dominant mechanism. Overall, our simulations establish molecular-level design rules for tuning the processability and rheology of dynamic covalent polymer networks via solvent quality.