Molecular Modulation Mechanisms of Strength–Toughness Performance in Long-Chain Branched Polyethylene

This study investigated the molecular modulation mechanisms underlying the high strength–toughness performance in long-chain branched polyethylene (LCBPE). Molecular dynamics simulations were employed to construct LCBPE systems with branch lengths ranging from one to four times the critical entanglement molecular weight (Me). The microstructural evolution of these systems during melt equilibration, crystallization, and tensile deformation was tracked to elucidate the structural foundations and molecular-level modulation mechanisms governing the strength–toughness performance. The results indicated that branch length in LCBPE exerted a nonmonotonic influence on the material’s strength–toughness performance. Within the tested parameter range, the material exhibited optimal mechanical performance when the chain length of the long-chain branch (LCB) was approximately twice the system’s critical Me. When the LCB length was below this threshold, although chain entanglement and tie-chain content increased compared to linear chains, they were insufficient to offset the negative impact of reduced crystallinity, manifesting as enhanced toughness and a reduction in peak stress. When the LCB length exceeded this threshold, the pronounced extensibility of the branches resulted in a less compact semicrystalline structure, which became more susceptible to interchain disentanglement under external loading. This structural change weakened the strain-hardening process and hindered the material’s ability to fully realize its strength–toughness potential.