Reduced Entanglement Density of Ultrahigh-Molecular-Weight Polyethylene Favored by the Isolated Immobilization on the MgCl2 (110) Plane

The polyhedral oligomeric silsesquioxane (POSS)-modified Ziegler–Natta catalysts with judicious immobilization of TiCl4 were synthesized for ethylene polymerization. The structure of active sites in this heterogeneous catalyst was investigated by X-ray photoelectron spectroscopy, CO low-temperature adsorption diffusion reflectance infrared Fourier transform (DRIFT) spectra, and density functional theory calculations. The incorporated POSS molecules contribute to the formation of the MgCl2 (110) plane, creating more positions for hosting the active sites. Simultaneously, POSS induced the crystallization of MgCl2 molecules, and the latter capture the deactivated TiCl4 molecules and consume part of the loaded TiCl4. This combination dilutes the active sites on the catalytic surface and gives rise to more isolated active species and results in enhanced catalytic activity and decrement of the chain overlap. As a result, the ultrahigh-molecular-weight polyethylene (UHMWPE) with a less entangled state was successfully synthesized at 80 °C, with exceptional activity (6.18 × 105 g PE molTi–1 h–1 bar–1). The synthesized UHMWPE presents less morphological defects after the fusion, thanks to the weakly entangled state, and shows a pronounced improvement of the impact property.