Highly active three-component catalytic systems based on dialkylzirconocenes, triisobutylaluminum, and perfluorophenyl borates for synthesis of low-molecular-weight polyethylene

The catalytic properties of the zirconium complex with "constrained geometr y" Me2SiCp*NBu(1)Zrx(2) (Cp* = C5Me4, X = Cl (1a), Me (1b)) and bridged bis (cyclopentadienyl)zirconocene Me2SiCp2ZrX2 (X = Cl (2a), Me (2b)) during th eir activation with triisobutylaluminum/perfluorophenyl berates (TIBA/LB(C6 F5)(4), L = CPh3 (3), Me2HNPh (4)) in ethylene polymerization under a monom er pressure of 2-20 atm were studied by comparison. Both dichloride complex es exhibit moderate activity under the action of the combined TIBA/3 activa ting agent and give linear high- molecular-weight polyethylene (PE). The in teraction of the dimethyl complexes with TIBA/3(4) afford active sites in w hich the growing polymeric chain is intensely transferred to the monomer, d ue to which low-molecular-weight PE is formed. The dichloride complexes aff ected by TIBA/4 also afford low-molecular-weight PE. Analysis of the struct ure of the polymeric products (H-1 NMR spectrometry, IR spectroscopy), mole cular-weight parameters of the PE samples (gel permeation chromatography (G PC)), and kinetics of polymerization suggested that the active site contain s AlBu3i as 3 heteronuclear bridged cationic complex. The influence of vari ous basic substrates (the products of chain transfer with the terminal viny l groups, the dimethylaniline fragment of berate 4 or other amine specially introduced into the reaction mixture) on the catalytic properties of the Z r-Al site was revealed. The polymerization rate and molecular-weight parame ters of PE as functions of the reaction temperature, ethylene pressure, and modifying additives were studied.