Preparation of Hexene-Ethylene Copolymers by the In Situ Copolymerization of Ethylene with Chromium trimerization Catalyst and Cp2(Ind)2ZrCl2

Methylaluminoxane (MAO)-activated chromium (III) complexes of tridentate SNS ligands of the form (RSCH2-CH2)2NH (R=alkyl or aryl) have been prepared in good yield and high purity using inexpensive reagents. Then the ligands reacted with CrCl3(THF)3 at room temperature to give the corresponding CrCl3/SNS catalysts in high yield. The catalysts were tested for the trimerization of ethylene to 1-hexene. An ethylene trimerization reaction at 90 °C and 23 bar ethylene, using the CrCl3/SNS complex activated by 700 equivalents of MAO, afforded 99.9 % 1-C6. Only 0.10 % PE was produced. The effect of ethylene pressure, Al/Cr ratio and S donor substitution on 1-C6 selectivity and productivity has been examined. Pentyl group on S lead to the highest activity, 174200 g 1-C6/g Cr h, due to the synergistic effect of this group. In the second section, effective tandem catalysis systems consisted of trimerization catalyst CrCl3/SNS and the copolymerization catalyst of Cp2(Ind)2ZrCl2 were developed. We used the system for the synthesis of ethylene-1-hexene copolymers under different ethylene pressure, Cr/Zr ratio. The activity of tandem polymerization increased with the Cr/Zr molar ratio. Successive increases in the CrCl3/SNS amount yielded a series of copolymer samples with decreased Tm and Xc. 13CNMR and 1HNMR results showed that the resulting copolymers contained only C4 side-chains.

کلیدواژه ها:

Ethylene ، Trimerization ، 1-Hexene ، Chromium catalyst ، Tandem