Influence of Modified Ziegler-Natta Catalyst on the Entanglement Behavior and Properties of Ultrahigh-Molecular-Weight Polyethylene (UHMWPE)

Different dealcoholizing methods and polyhedral oligomeric silsesquioxanes (POSS) were utilized for the modification of Ziegler-Natta catalysts. Their effects on the properties of the catalysts and the synthesized ultrahigh-molecular-weight poly-ethylene (UHMWPE) were thoroughly studied. It was found that physical dealcoholization of the magnesium chloride-ethanol adducts increased the specific surface area (SSA) of the catalysts more effectively than chemical dealcoholization, expanding the contact area between active centers and ethylene. Thus, better catalytic activity was induced. The sufficient distance between growing chains is the key point in the entanglement degree of UHMWPE. With the load of TiCl4, physical dealcoholized catalysts always provide greater spacing between growing chains, decreasing the potential of segment tangling, and that matches the less-entangled state of the synthesized UHMWPE determined by the initial storage modulus by a rotary rheometer. The modification of the catalysts by polyhedral oligomeric silsesquioxanes (POSS) was also studied, and it was discovered that POSS shows little effect on catalytic activity. However, POSS-modified catalysts limited the active centers to a closer range. Coupled with the strong interaction between UHMWPE and POSS particles, UHMWPE with a higher entanglement state were produced. The crystallization behavior and mechanical properties of the obtained UHMWPE were also studied.