A Reactive Bead-Spring Model for Associative Polymer Melts In and Out of Equilibrium

We describe a new coarse-grained reactive molecular dynamics model for associative polymer networks. Our model combines a Tersoff bond-order potential for associative bond chemistry with a standard bead-spring model for molten polymers. The resulting model captures the essential physics of chain dynamics, chain entanglement, and coordinated dynamic bonding and can be tuned to capture a variety of associative bond kinetics. The many-body Tersoff Hamiltonian for dynamic bonding remains valid in nonequilibrium flow conditions, unlike Monte Carlo methods based on equilibrium bond kinetics. We use this model to simulate polymer melts with binary associative bonds of varying cohesive strength. We measure the gelation transition with increasing association strength and identify a gel point at an associative bond strength similar to 1k(B)T. We also assess how chain dynamics and network viscoelasticity change as the degree of gelation increases and relate them to the microscopic kinetics of dynamic bond exchange.