Imido-modified SiO2-supported Ti/Mg Ziegler-Natta catalysts for ethylene polymerization and ethylene/1-hexene copolymerization

A novel imido-modified SiO2-supported Ti/Mg Ziegler-Natta catalyst for ethylene and ethylene/1-hexene polymerization is investigated. The catalyst is prepared by modification of (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts via supporting vanadium species followed by reaction with p-tolyl isocyanate as imido agents, to get the merits from both the SiO2-supported imido vanadium catalyst and the (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalyst. The effects of cocatalyst amount, hydrogen and dosage of 1-hexene on polymerization behavior and the microstructures of their polymers are systematically investigated. Compared with (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts and vanadium-modified (SiO2/MgO/MgCl2)TiClx Ziegler-Natta catalysts, the imido-modified SiO2-supported Ti/Mg catalysts show lower but more stable activity including homopolymerization, polymerization with hydrogen and copolymerization owing to imido ligands, indicating that p-Tolyl isocyanate was unfavorable to improving catalytic activity but benefited the stability, and the products of all catalysts show lower 1-hexene incorporation but much higher molecular weight (MW) with medium molecular weight distribution (MWD). The most unique feature of the novel catalysts is the excellent hydrogen response without lowering the polymerization activity, showing great potential for industrial application.