Ternary Metallocene Based Catalysts in High Temperature, High Pressure Polymerization

The polymerization of 1-hexene under high pressures (100 -750 MPa) was investigated with nickel-␣-diimine complex/methylaluminoxane and palladium-␣-diimine complex/methylaluminoxane as catalyst systems. The catalytic activity of both the nickel and palladium complexes monotonously increased as pressure rose and became two to four times higher than that observed at atmospheric pressure. Palladium catalysts gave poly(1-hexene)s with higher molecular weights under high pressure, whereas nickel-catalyzed high-pressure polymerizations gave polymers with higher molecular weights only at rather low monomer concentrations. The living-like character in the palladium-catalyzed polymerizations was somewhat enhanced under higher pressures, whereas the nickel-catalyzed polymerizations under high pressures were not living. More branches were found in the polymers produced by nickel catalysts at higher pressures. The chain-transfer reaction seemed to be accelerated by the high pressure in the nickel-catalyzed reactions, although this was not apparent in the palladium-catalyzed reactions. Dimers formed and were accompanied by high molecular weight polymers when nickel catalysts were used under high pressures and at high monomer concentrations. The possibility that very congested five-coordinated species act as key intermediates for the dimerization is discussed.

Nickel‐ and palladium‐catalyzed olefin polymerization under high pressures

Suzuki

Masubuchi

et al. 2002

Triisobutylaluminum as cocatalyst for zirconocenes. I. Sterically opened zirconocene/triisobutylaluminum/perfluorophenylborate as highly effective ternary catalytic system for synthesis of low molecular weight polyethylenes

Панин

Sukhova

Bravaya

2001

Ethylene polymerizations with catalytic systems Me2SiCp*NtBuZrX2 (1) [Cp* = C5(CH3)4; X = Cl (1Cl), Me (1Me)], triisobutylaluminum (TIBA), perfluorophenylborate CatB(C6F5)4 [Cat = CPh3 (3), Me2NHPh (4)], or Me2SiCp2ZrX2 [X = Cl (2Cl), Me (2Me)]/TIBA/3 (4) were performed within a wide range of ethylene pressures of different Al/Zr ratios, and Zr/B = 1. Catalytic systems 1Cl(2Cl)/TIBA/3 led to the formation of very high linear molecular weight polyethylene (PE) of Mη ∼2,000,000 with low activity. The replacement of both chlorine ligands in the precatalyst for the methyl ones led to the formation of active species producing low molecular weight PE with high activity. Chain transfer to ethylene was shown to be the main reaction controlling PE chain propagation: kp/ktr ∼20–30 for 1Me/TIBA/3 and kp/ktr ∼350–500 for 2Me/TIBA/3. It was suggested that TIBA was present in the active center first in the form of a neutral heterobimetallic Zr–Al bridged complex followed by the formation of a partially polarized Zr–Al(Cl)R2 (R = iBu) or an unreactive Zr–AlR3 cationic complex by abstraction of the alkyl ligand under the action of borate. It was concluded that AlR3 from the latter cationic complex may be easily reversibly replaced under the specific coordination of ethylene or accumulated α‐olefin, giving rise to highly labile and sterically accessible cationic species. Experiments on ethylene polymerization with the catalytic systems 1Cl(1Me)/TIBA/3/Ph2NH, 1Cl(1Me)/TIBA/4, 2Cl(2Me)/TIBA/3/Ph2NH, and 2Cl(2Me)/TIBA/4 were performed to confirm the suggestion. Catalytic systems derived from dichloride complexes in the presence of a σ‐donor substrate also produced low molecular weight PEs with molecular weight characteristics similar to those of products obtained with the dimethylated precatalysts. The specific feature of active species derived from 2Me complexes to isomerize coordinated α‐olefin into trans‐vinylene polymer chains was also revealed. The catalytic behavior of the ternary catalytic system based on 2Me relative to 2Me or 2Cl precatalysts activated with polymethylaluminoxane at different Al/Zr ratios was compared. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1901–1914, 2001

Triisobutylaluminum as cocatalyst for zirconocenes. II. Triisobutylaluminum as a component of a cocatalyst system and as an effective cocatalyst for olefin polymerization derived from dimethylated zirconocenes

Панин

Джабиева

Недорезова

et al. 2001

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