An investigation of the catalytic behavior of the dimethylated zirconocenes Me2SiCp*NtBuZrMe2 [Cp* = C5(CH3)4; 1Me], Me2SiCp2ZrMe2 (2Me), Cp2ZrMe2 (3Me), Ind2ZrMe2 (4Me), Me2SiInd2ZrMe2 (5Me), Et(2‐MeInd)2ZrMe2 (6Me), and Me2Si(2‐MeInd)2ZrMe2 (7Me) with the combined activator triisobutylaluminum (TIBA)/CPh3B(C6F5)4 (Al/Zr = 250; B/Zr = 1) in ethylene polymerizations at increased monomer pressures (5–11 bar, 30 °C) was carried out. Sterically opened zirconocenes in ternary catalysts gave rise to active species effective in the formation of low molecular weight polyethylenes (PEs). These active species tended to increase the PE molecular weight [1Me (2100) < 2Me (20,000) < 5Me (89,000) < 3Me (94,500)] under similar conditions. PE obtained with 4Me showed a bimodal gel permeation chromatography curve with a 64% peak area [weight‐average molecular weight (Mw) = 43,000] and a 36% peak area (Mw = 255,000). The increase in sterical demands from the zirconocenes was also demonstrated by the reduction of the chain transfer to monomer, the reinsertion of vinyl‐ended PE chains, and their ability for isomerization. These reactions were most pronounced for the zirconocenes 1Me and 2Me. The active species responsible for the formation of low molecular weight PEs deactivated quickly. The zirconocenes 6Me, 7Me, and (2‐PhInd)2ZrMe2 (8Me) bearing substituent at the 2‐position of the indenyl ring was activated with TIBA alone, yielding active species effective in ethylene and propylene polymerizations. PEs formed with 6Me–8Me complexes activated with TIBA had high molecular weights. An increase in the Al/Zr ratio in the catalytic system 8Me/TIBA from 50 to 300 led to an enhancement of the molecular weight of polypropylene (PP) samples from oligomeric products to an viscosity‐average molecular weight of 220,000. The increase in the molecular weights of PPs with an increase in the propylene concentration was also observed. An analysis of the catalytic performance of the 8Me/TIBA system showed first‐order dependency of the initial polymerization rates on the TIBA concentration and close to second‐order dependency on propylene. The second‐order dependency on the monomer concentration is explained in terms of the monomer participation in the initiation step of the polymerization reaction. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1915–1930, 2001

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Comparative analysis of catalytic activity of substituted bis(cyclopentadienyl)zirconium dichlorides with the general formula (RnCp)2ZrCI 2 (CP2ZrCI2, (MeCp)2ZrCI2, (PriCP)2ZrCI2, (pri2Cp)2ZrCl2, (BunCP)2ZrCl2, (BuiCP)2ZrCI2, (ButCP)2ZrCI2, CP*2ZrCI 2 (Cp* = MesCs), (Me3SiCp)2ZrCI2, 2Cpl2ZrCl2) in ethene polymerization using polymethylalumoxane as the cocatalyst was performed. The molecular mass characteristics of the polyethylene samples obtained were determined. A linear correlation of the specific activity of the catalysts and the turnover number with the electronic and steric characteristics of substituents at the Cp ring of the complexes was established for the first time. Analysis of the polymerization kinetics and the obtained correlation between the specific activity of the complexes and molecular mass characteristics of the polyethylene samples suggest that alkyl substituents participate in reactions responsible for the restriction of the polymer chain growth and regeneration of the active center. These interactions most likely involve associates of AIMe 3 with polymethylalumoxane molecules.Key words: metallocene complexes, bis(cyclopentadienyl)zirconium dichlorides, effect of substituents, ethene polymerization.Many experimental and calculation works are devoted to the effect of substituents on the reactivity of substituted zirconium and titanium bis(cyclopentadienyl) complexes in olefin polymerization in the presence of the cocatalyst, polymethylalumoxane (MAO). However, it is difficult to compare the catalytic properties of the metalloeene dichloride--MAO systems described by different authors, because these very efficient catalysts are very sensitive to experimental conditions (purity of reagents, concentration and order of introducing components of the catalytic system, pressure of the monomer, AI/Zr ratio, etc.). The eiTect of substituents was analyzed in most detail in the recent review, t As for cyclopentadienyl complexes, an increase in the catalytic activity of the catalyst and molecular mass of the polymer when alkyl substituents are introduced into the ring was mentioned in several works, z:6 Data on the effect of substituents are discussed at the qualitative level, as a rule, in terms of the electronic and steric effects of substituents. However, analyses of experimental results are often contradictory. For example, the explanation of the effect of electron-donor substituents in the cyclopentadienyl ring on the,activity of the M--C bond in Ref. I is reduced, in particular, to the fact that "these substituents decrease the positive charge on the metal, thus weakening bonds of the metal with other ligands, inchtding the M--C bond" at which olcfin is inserted during polymerization. At the same time, the cyclotron-resonance mass spectrometric study of the ion-molecular reactions of L2ZrCH3 + with H 2 ar~l C2H 4, where L 2 = CpCp, Cplnd, lnd 2, and Flu 2 (Cp is cyclopentadienyl, lnd is indenyl, and Flu is fluorenyl) are substituents, whose donating capability increases in the series indicated, sh...

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