Unraveling the influential mechanism of short-chain branching on the crystallization of trimodal polyethylene by molecular dynamics simulation

Trimodal polyethylene (PE) has become the focus of research in recent years due to its excellent performance. By means of molecular dynamics simulations, we aim to expound the molecular mechanism of short-chain branching (SCB) in the nucleation process, crystallization process and chain entanglement of trimodal PE. In this study, a series of polyethylene models including different short-chain branching concentrations (SCBCs), short-chain branching lengths (SCBLs), and short-chain branching distributions (SCBDs) were considered. The increase of SCBCs greatly reduces the ability of flipping and movement of PE chains, resulting in more time for nucleation and crystallization and a significant reduction of crystallinity. In contrast, an increase in the SCBL only slightly slows down the diffusion rate of the chain, which leads to a little increase in crystallization time. Most important of all, in the study of SCBD, we find that the distribution of SCBs on a high molecular weight chain, which is the characteristic of trimodal PE, is conducive to the chain entanglement and prevents the occurrence of micro phase separation compared with the case where the SCBs are distributed on a medium molecular weight chain. The mechanism of chain entanglement is proposed to explain the effect of SCBs on tie chain entanglement.

Automated summary

Through molecular dynamics simulations, we investigated the molecular mechanism of short-chain branching (SCB) in the nucleation process, crystallization process, and chain entanglement of trimodal polyethylene (PE). Our results reveal that an increase in SCB concentration significantly hinders the flipping and movement of PE chains, leading to prolonged nucleation and crystallization time and reduced crystallinity. On the other hand, an increase in SCB length only slightly slows down chain diffusion rate and slightly increases crystallization time. Additionally, we find that the distribution of SCBs on high molecular weight chains in trimodal PE promotes chain entanglement and prevents micro phase separation, unlike when SCBs are distributed on medium molecular weight chains.