Chen Zou

The long-term stability of various polyolefins relies on antioxidants. Traditional methods such as physical blending or chemical modification often suffer from non-uniform dispersion, migration, or lack of universality, especially for ultra-high molecular weight polyethylene (UHMWPE). Developing a general strategy to access various polyethylene types bearing intrinsically antioxidant properties (defined as polyolefins with antioxidant properties produced via polymerization, without postpolymerization antioxidant addition) remains a challenge. Here, we present a Catalyst-Enabled Antioxidation Strategy (CEAS) using phenolic hydroxy-functionalized dual-functional catalysts that both catalyze polymerization and provide antioxidant capacity, enabling the production of various types of intrinsically antioxidant polyolefins. We further develop enhancement strategies via auxiliary antioxidants and biomass-supported heterogeneous catalysis to boost antioxidant properties. This approach ensures uniform dispersion, overcomes processing limitations, retains mechanical properties, and enhances antioxidant performance. Notably, CEAS-synthesized UHMWPE demonstrates resistance to oxidation during demanding processing such as high-temperature spinning and radiation-induced crosslinking.

The performance regulation of polyolefin catalysts typically relies on complex ligand design and synthesis, which limits the rapid development of high-performance polyolefins. The heterogenization of homogeneous catalysts presents a promising and industrially favorable approach to modulate and enhance the performance of transition-metal catalysts. This work introduces a general ionic cluster catalyst assembly (ICCA) strategy to achieve efficient in situ heterogenization without the need for any catalyst supports. It transforms known hydroxyl-functionalized transition-metal catalysts into ionic cluster assemblies by a simple one-step reaction. The steric hindrance of the catalyst metal center can be easily tuned by varying the feed ratios for assembly, without requiring the synthesis of new catalysts. This ICCA strategy enables up to 20 times higher activity during ethylene homo- and copolymerization while significantly improving the molecular weight and mechanical properties of the resulting copolymers. Furthermore, the in situ heterogeneous polymerization facilitated by this strategy demonstrates efficient heat transfer, lower system viscosity, and excellent fouling resistance during polymerization, indicating great potentials for scale-up polymerization. This work provides a general and efficient platform for tuning polyolefin catalyst performance.

Phosphine–phenolate nickel catalysts, based on [P, O] ligand, attracted much attention for its ability in catalyzing the copolymerization of ethylene with polar monomers. Herein, a series of tert ‐butyl substituted phosphine‐phenolate nickel complexes were synthesized and exhibited good catalytic performance in ethylene polymerization. Simultaneously, the molecular weight of the polyethylene products can be altered by steric and electronic perturb. In the copolymerization of ethylene with tert ‐butyl acrylate, methyl 10‐undecenoate and 6‐chlorohex‐1‐ene, these phosphine‐phenolate nickel catalysts yielded copolymers with tunable comonomer incorporation ratio (0.6‐2.0 mol%).

Among various polyolefin products, bimodal polyethylene is widely used as an important polyolefin, which is usually composed of high molecular weight polyethylene and low molecular weight polyethylene, however, having both components with different molecular weights and branching densities often increases the complexity of the polymerization process. In this work, we used a co-anchoring strategy to achieve co-supporting of α-diimine nickel catalyst and pyridine imine nickel catalyst, prepared bimodal (polar) polyethylene with different molecular weights and branching densities using only ethylene as a single feedstock. This bimodal polyethylene exhibited excellent mechanical properties, rheological properties and barrier properties. This strategy is expected to provide a new approach for preparing high-performance polyolefins with multiple microstructures.

Mechanical recycling of waste plastics is one of the main strategies for addressing plastic pollution, but most waste plastics exist as incompatible mixed plastics that undergo phase separation, making their direct mechanical recycling challenging. Here, a supramolecular dynamic cross-linking strategy using only a small amount of supramolecular dynamic small-molecule cross-linkers was designed to compatibilize and directly mechanically recycle a variety of nonpolar/nonpolar, nonpolar/polar, and polar/polar polymer blends. These difunctional small-molecule cross-linkers contain functional groups with supramolecular dynamic cross-linking capability and functional groups that can be easily grafted to various polymers. Under industrial processing conditions (reactive extrusion using a twin-screw extruder), these small-molecule cross-linkers can be grafted to both components of the mixed plastics. This leads to the in situ formation of a dynamic-cross-linked network that significantly improves the mechanical properties of the blends. More importantly, this strategy achieved the large-scale and multiple recycling/reuse of postconsumer mixed plastics using commercially available small-molecule cross-linkers.

Recently, a series of inexpensive nickel‐based phosphine phenol catalysts have been synthesized for catalyzing the copolymerization of ethylene and polar monomers to prepare functionalized polyolefins. However, it is still challenging to achieve homogeneous nickel catalysts that catalyze ethylene polymerization or copolymerization at high temperatures (up to 150°C) with high activity. This work synthesized a series of phosphine phenol nickel catalysts with bulky steric hindrance and electron donating groups, which were used for catalyzing ethylene polymerization and coordination copolymerization of ethylene and a series of polar monomers at high temperatures. These nickel catalysts exhibited high ethylene polymerization activity and excellent thermal stability at 150°C, producing polyethylene with a molecular weight of up to 102.7 × 10⁴ g mol⁻¹. More importantly, these catalysts can catalyze the copolymerization of ethylene and a range of polar monomers at 120°C, improving the surface properties of polyolefins.