Topology and Mechanical Properties of Polymer Networks Formed under Free Radical and Atom Transfer Radical Polymerizations

We present the results of a study that combines reactive Monte Carlo with coarse-grained molecular dynamics simulations to compare the kinetic evolution, topology, and mechanical properties of polymer networks synthesized by free radical (FRP) and atom transfer radical (ATRP) polymerizations. In both reaction schemes, the polymer networks were assumed to form by the bulk copolymerization of mono- and divinyl monomers, and the concentration of cross-linkers was varied. We analyzed the network topology by determining the distributions of elastically effective strands, dangling chains, and primary and higher-order loops. We find that, at a specified cross-linker concentration, FRP results in networks with more elastically effective strands, fewer dangling chains, and fewer primary loops compared to ATRP. In addition, we demonstrate that the differences in topological properties between these networks arise from the relative ratio of the rate of monomer diffusion to the rate of chain propagation. Through analysis of the true stress-elongation responses obtained from molecular dynamics simulations, we demonstrate that networks synthesized by FRP are stiffer and less extensible than their ATRP counterparts. Our results demonstrate the impact of copolymerization mechanisms on the topology and mechanical properties of polymer networks.