Ethylene/1-hexene copolymerization with MgCl2-supported Ziegler-Natta catalysts containing aryloxy ligands. Part I: Catalysts prepared by immobilizing TiCl3(OAr) onto MgCl2 in batch reaction

Novel aryloxy-containing MgCl2-supported Ziegler-Natta catalysts were prepared by treating TiCl3(OAr) (Ar = C6H5-, 2,6-Me2C6H3-, 2,6-i-Pr2C6H3-, 2,6-t-Bu2C6H3-) with MgCl2 in batch reaction. The influences of aryloxy group on the titanium content and aryloxy/Ti molar ratio in the catalysts was investigated. Because of ligand exchanges between the immobilized titanium species and TiCl3(OAr) in the solution, the aryloxy/Ti molar ratio in these catalysts were less than 1. Using triethylaluminum (TEA) or triisobutylaluminum (TIBA) as cocatalyst, these catalysts showed different catalytic behaviors in ethylene-1-hexene copolymerization. Using TIBA as cocatalyst, the aryloxy-containing catalysts showed higher activity than a TiCl4/MgCl2 blank catalyst. Although the total 1-hexene incorporation of the copolymers prepared by the novel catalysts were lower than that of the blank system, the difference in 1-hexene content between the boiling n-heptane soluble part and the insoluble part was markedly lower, and the blockiness of comonomer sequence distribution was evidently higher. The TIBA activated aryloxy-containing catalysts were found to produce poly(ethylene-co-1-hexene) with more uniform chemical composition distribution. (C) 2012 Elsevier B.V. All rights reserved.