Controlled Chain-Walking Polymerization in the Gas Phase to Ultrahigh Molecular Weight Polyethylene

This study presents an unconventional approach for the gas-phase synthesis of ultrahigh molecular weight polyethylene (UHMWPE) using sterically hindered 2,6-bis-(diarylmethyl) α-diimine palladium-(II) catalysts. By leveraging a self-supported chain-walking polymerization mechanism, the catalysts form thin films on reactor walls, enabling efficient ethylene polymerization without solvents. The gas-phase chain-walking mechanism facilitates the migration of palladium species within the porous polymer matrix, enabling them to locate and access optimal sites for ethylene capture and subsequent insertion. The distal substituents on the catalysts were systematically varied to investigate their electronic and steric effects on polymerization activity, molecular weight, and branching density. Under optimized conditions (6 atm ethylene, 25 °C), the catalysts achieved high activity (up to 3.90 × 10⁵ g/(mol·h)) and produced UHMWPE with molecular weights exceeding 1600 kg/mol. Kinetic studies revealed a unique three-stage polymerization process, while branching densities (29-131 branches/1000 C) were tunable via catalyst design. The resulting polyethylene exhibited a porous network morphology and balanced mechanical properties, combining high impact resistance with processability. This work highlights the potential of gas-phase polymerization as an environmentally friendly and cost-effective route to UHMWPE with tailored microstructures.