Flow-Driven Dynamic Heterogeneity in Elongating Associative Polymer Networks

Associating polymers form dynamic networks of reversible bonds that can rearrange their network topology. These transient networks can form mechanically durable materials that remain - in principle - reprocessable and recyclable. However, the nonequilibrium dynamics of associative networks are challenging to predict and control, making practical reprocessing difficult. The constant rearrangement of dynamic bonds in the associating network produces a complex coupling between the relaxation modes of individual chains that carry stress and the surrounding self-assembled network that mediates strain from the macroscopic to the molecular scale. Understanding these dynamics requires models that can capture the feedback between dynamic bonding and polymer relaxation in nonequilibrium conditions. Here we apply a new reactive bead-spring model for associating polymers with coordinated dynamic bonds and study their dynamics during extensional deformation. We model the rate-dependent response of associative networks formed from linear polymers with binary associative groups for a wide range of associative bond strengths. We observe that the coupling between chain and network relaxation drives a strong heterogeneity in chain elongation during deformation, producing broad distributions of chain stretch at all strain rates. This broad nonlinear response cannot be described by average order parameters used in established molecular theories of polymer dynamics, motivating the need for new physical models for associative polymers.