Coarse-grained simulations on the crystallization, melting and annealing processes, of short chain branched polyolefins

Coarse-grained molecular dynamics simulations studies on supercooled linear and short chain branched polyethylene melts are reported. This is the first time that a coarse grained simulation study is carried out on the crystallization process of short chain branched polyethylenes. Crystallization and subsequent melting temperatures are related linearly to the inverse of the lamellar thickness. Different melting lines, depending on short chain branching content are obtained, but a tendency to a single crystallization line is observed. These results qualitatively match to the experimental lines obtained in model homogeneous ethylene/alpha-olefin copolymers. Additionally, a strong lamellar thickening process is reported for the linear model at temperatures below the melting point, which follows the classical interpretation reported in polyethylene, with a logarithmic increase of the crystal thickness with time. However, for the branched samples the thickening is impeded at the same degree of undercooling. In the branched models the short chain branches are excluded from the crystal remaining at the surface and amorphous regions. This causes the pinning of these regions, minimizing crystal chain diffusion and hindering crystal stem thickening. Again the simulated results qualitatively agree with the experimental data.(C) 2016 Elsevier Ltd. All rights reserved.