Molecular dynamics simulation study of the influence of branch content on crystallization of branched polyethylene chains with uniform branch distribution

Linear low-density polyethylene (LLDPE) chains with different levels of branch content (BC), ranging from 10 to 80 branches/1000 C, distributed uniformly along the chain are theoretically simulated in vacuum at a temperature of 350K using molecular dynamics. The influence of BC on the relaxation and crystallization of LLDPE chains is studied. Ethylene-octene copolymer chains were modeled as chains composed of united atoms where each CH, CH₂ and CH₃ is represented by a single spherical segment. The collapse of the branched chains is found to occur via a local followed by a global collapse mechanism with branches acting as nucleation points for the collapse of the molecule leading to faster collapse of chains with higher BC. The trans population is found to be dominant at all branch contents; however, it decreases with increasing BC. Increasing BC is found to decrease order and to strongly influence chain conformation. Chain. conformation undergoes a transition from lamellar to a more random coil-like structure near a critical BC of 50 branches/1000 C. Branches are observed to be excluded from the lamella and to self assemble at high BC. This work also provides insight into the conformation adopted during the coil-globule transition experienced by a single chain in an infinitely dilute solution much below the θ temperature. This study is purely theoretical and no attempt was done to verify the results of this work experimentally.