Leveraging Dynamic Bonds to Probe Equilibrium Topology in Polymer Networks

Formation of chemically crosslinked polymer networks is a kinetically driven process leading to local topological defects such as primary loops, which decrease elastic effectiveness. Dynamic bonds in a network create possibilities for bond exchange and network rearrangement, potentially altering topology. This work investigates how network topology changes as a result of incorporating dynamic bond rearrangements into an irreversibly cross-linked network. A Kinetic Monte Carlo simulation framework was developed to model reversible bond exchange in permanently crosslinked networks. The evolution of network topology was studied during a three-step process: network formation, equilibration, and recovery. Networks were characterized by their higher order cyclic topology, using a computationally efficient algorithm based on the mathematics of 3D nets. Simulations and experimental validation reveal that incorporating dynamic bond rearrangements leads to lower primary loop fraction and higher modulus. Such rearrangements lead to the formation of a more strongly percolated structure and a greater number of higher-ordered cyclic structures in comparison to kinetically crosslinked networks. The quantitative change in topology is dependent on the concentration and equilibrium constant, demonstrating that irreversible cross-linking occurs by an out-of-equilibrium process and that dynamic bonding can tune network topology.