Covalent Organic Framework-Oriented Chain Growth for High-Performance Polyolefins

Polyolefins have long dominated materials technology and polymer production; yet enhancing mechanical strength, toughness, and processability in high-performance polyolefins still remains a challenge. Herein, we use minimal quantities of covalent organic frameworks (COFs) to engineer the native aggregate structure of polyethylene (PE). By employing in situ ethylene polymerization, we synthesized high-performance COF-PE composites with unique nanofibrous structures at COF loadings of 0.02 wt %. Specifically, hydroxyl-functionalized imine-based COFs act as macroligands for bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂), establishing a unique spatial confinement on chain growth. The resulting COF-PE composite exhibits a weight-average molecular weight (M_w) of up to 240.0 kDa (increasing 118%), a narrow molecular weight distribution (Đ as low as 1.9), and an elevated melting point (T_m) of 139.2 °C (4.5 °C higher) compared to pure PE. Moreover, the composite exhibits an outstanding tensile strength of 45.5 MPa and an unprecedented elongation at break of 1832%, outperforming both literature-reported and commercial counterparts. Remarkably, it demonstrates enhanced melt processability above T_m, evidenced by a reduced zero-shear viscosity (η₀) of 3953 Pa·s. Structural analyses reveal COF rigidity-dependent crystalline reinforcement, featuring thickened lamellae (15.1–17.0 nm) and tunable nanofibrous diameters (123–512 nm). This work demonstrates COF-immobilized catalysts enabling polyolefin nanostructural engineering for simultaneous mechanical enhancement and processing optimization.