Gas-Phase Synthesis of Hyperbranched UHMWPE by Enhancing Chain Walking and Minimizing Chain Transfer

A series of rigid-flexible unsymmetrical bulky α-diimine palladium catalysts was employed for the gas-phase polymerization of ethylene, enabling the synthesis of hyperbranched ultrahigh molecular weight polyethylene (UHMWPE). Compared to conventional solution-phase polymerization, the gas-phase method significantly suppresses chain transfer while promoting chain walking, leading to a simultaneous increase in both molecular weight and branching density. Under optimized conditions, the resulting polyethylene exhibited high molecular weight (up to 2053 kg/mol) and branching densities as high as 107 branches per 1000 carbon atoms. Structural characterization confirmed the presence of long-chain branches and branch-on-branch architectures, indicative of a hyperbranched topology. The unsymmetrical palladium catalysts produced polyethylene with higher molecular weight and branching density than the benchmark catalysts, by combining suppressed chain transfer with high chain-walking ability. This work demonstrates the potential of gas-phase polymerization as a solvent-free, environmentally benign route to advanced polyolefin materials with tailored architectures.