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 ( M e ). 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 M e . 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.