Preparation of LLDPE through tandem ethylene polymerization using chromium and zirconium catalysts

The effective tandem catalysis systems including the trimerization catalyst of CrCl3/SNS [SNS = bis-(2-pentylsulfanyl-ethyl)-amine] and the copolymerization catalyst of rac-ethylene bis(indenyl) zirconium (IV) dichloride have been introduced. The CrCl3/SNS catalyst was synthesized via reaction between CrCl3(THF)(3) precursor and SNS as efficient ligand at room temperature. An ethylene trimerization reaction at 90 degrees C and 23 bar ethylene, using the CrCl3/SNS complex activated by 700 equivalents of methylaluminoxane, afforded 99.9 % 1-C6. Only 0.10 % PE was produced. Effect of different parameters such as ethylene pressure and Cr/Zr ratio was investigated during tandem polymerization. Successive increases in the CrCl3/SNS amount yielded a series of copolymer samples with decreased T-m and X-c. The butyl branches of produced polymer were identified by C-13 NMR analysis. Data from dynamic mechanical thermal analysis indicated formation of various polymeric materials with the branches, which their stiffness varied according to the Cr/Zr ratio used in the polymerization reaction.