Molecular dynamics simulation of the linear low-density polyethylene crystallization

By means of molecular dynamics simulation, the crystallization process of the copolymer (ethylene-co-propene) with different branch distributions is studied at the molecular level. It is shown that subglobules formed at the branch sites along the copolymer chains and subsequently coalesced into a single globule and then developed to a lamellar structure in the end. This process can be considered as crystal nucleation and growth at the early stage of the copolymer crystallization. In the nucleation the branch acts as a nucleating seed and in the crystal growth the branch is rejected from the crystal region as a defect. The driving force for the relaxation process is the attractive van der Waals interaction between the chain segments. Furthermore, it is found that the branch distribution is an important factor in determining the crystallinity of the copolymer, when the comonomer composition and the molecular weight of the copolymers are fixed, as a blocky type of copolymer will show nearly unhampered crystallization and a true random copolymer will show a hindered one.