Segmental Dynamics Revealed from All-atom Simulations of Concatenated Polyethylene Rings

Predicting entanglement molecular weight from all-atom simulations remains challenging. We present all-atom MD simulation results for concatenated rings of polyethylenes with up to 1600 carbon atoms. The chain-end effects are suppressed, and the entanglement topology is equilibrated by temporarily turning off and on the intermolecular pairing potential that prevents chain segments to cross. The bead mean squared displacement and stress relaxation data covering the reptation plateau are reported, and are analyzed using the tube model adapted to ring polymers. It is found that the monomer relaxation is slowed down substantially by angle and dihedral restrictions. A characteristic subdiffusion 3/4 scaling around the entanglement time is identified for all molecular weights investigated, which supersedes the 1/2 Rouse scaling expected for flexible chains.