The presence of a small amount of short chain branching along the polymer chain in commercially available linear low density polyethylene (LLDPE) grade plastics imparts exceptional toughness and flexibility to the material. One can obtain a wide range of desirable properties in such materials by fine-tuning the co-monomer content and the length of side branches. The influence of branching on the molecular level organization in the semi-crystalline interphase, which in turn affects the thermo-mechanical properties of the material, has defied detailed examination to date. In this presentation we describe our development of an accurate molecular level model of semi-crystalline polyethylene with short chain branches. This model explicitly takes into account the interphase present within the lamellar crystal stacks and can accurately describe the various chain topologies (loops, tails, and bridges) and the experimentally observed thermo-physical properties. We use Monte Carlo (MC) simulations, combined with advanced configurational bias, end-bridging and other efficient MC moves designed for polymeric systems, to sample the metastable equilibrium ensemble associated with branched semi-crystalline polyethylene. We examine three branched systems containing ethylene co-polymerized with propene, butene or heptene. We present our results on the effect of co-monomer content and length of branches on the structure and morphology of the interphase. The simulations reveal how branches distribute in the interlamellar region and whether they segregate near the crystal surface, as suggested by some experiments. They also provide insight into the influence of branching on the lengths and population distributions of various chain topologies, the profiles of orientational order and density, and conformations of the chain backbone.

Effect of short chain branching on the properties of semi-crystalline polyethylene

249th National Meeting (2015)

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