(692a) Effects of Entanglement on Polyethylene Crystal Nucleation and Growth

We employ united-atom molecular dynamics simulations to quantify the roles of entanglement in polyethylene crystal nucleation and growth under quiescent conditions. To study the effect of polymer entanglement on crystal nucleation, we use cyclic polymers and compressed linear chains. Unlinked rings do not exhibit any conventional entanglement topology and randomly concatenated rings are "permanently" entangled and cannot fully relax. By isotropically compressing individual polymer chains, we reduce the inter-molecular contacts and hence the entanglement in polymer melts. After demonstrating that the linear and cyclic chains exhibit similar crystal melting temperatures, we show the isothermal crystal nucleation rate of PE increases mildly with decreasing entanglement density. When the critical nucleus is smaller than the entanglement strand, the formation of a critical nucleus is not strongly impacted by entanglement. Nonetheless, we expect the topological interactions to affect crystal growth and the formation of final semicrystalline morphologies of polymer samples. By crystallizing PE melts onto post-critical crystalline seeds, we study the role of entanglement in long-time polymer crystal growth. Together with primitive path analysis (PPA), MD simulations allow us to track the formation of entangled tie-chains and loops during crystal growth as functions of polymer molecular weight and long periods of semicrystalline structures. By analyzing the spatial distributions of polymer entanglements, we show that trapped entanglement strands formed by loops and ties accumulate over time around polymer crystals, in turn hindering the propagation of crystalline order in the samples.