Molecular Simulations of Controlled Polymer Crystallization in Polyethylene

Multilamella polymer crystals are grown from the meltfor the firsttime, in molecular dynamics simulations of a united-monomer model,with in excess of 1500000 united-monomers. Two-component systems comprisedof equal weight fractions of 2000 united-monomer long chains and 200united-monomer short chains are considered, with varying numbers ofshort butyl branches placed along the long chains. Utilizing two differentcooling protocols, continuous-cooling and self-seeding, drastically different multilamellastructures are revealed, which depend heavily on the branch contentand crystallization protocol used. By self-seeding, well-aligned multilamellacrystals are grown, which more clearly reveal the subtle alterationsan increasing number of branches create on the size and shape of thecrystallites in the early stages of spherulite formation. Under continuouscooling, this observation is almost completely obscured. At maximumthickness, chain portions as long as 100 united-monomers (200 carbons)are extended inside the crystalline lamella.