Petri Lehmus

Influence of the catalyst and polymerization conditions on the long‐chain branching of metallocene‐catalyzed polyethenes

A study was made on the effects of polymerization conditions on the long-chain branching, molecular weight, and end-group types of polyethene produced with the metallocene-catalyst systems Et[Ind]2ZrCl2/MAO, Et[IndH4]2ZrCl2/MAO, and (n-BuCp)2ZrCl2/MAO. Long-chain branching in the polyethenes, as measured by dynamic rheometry, depended heavily on the catalyst and polymerization conditions. In a semibatch flow reactor, the level of branching in the polyethenes produced with Et[Ind]2ZrCl2/MAO increased as the ethene concentration decreased or the polymerization time increased. The introduction of hydrogen or comonomer suppressed branching. Under similar polymerization conditions, the two other catalyst systems, (n-BuCp)2ZrCl2/MAO and Et[IndH4]2ZrCl2/MAO, produced linear or only slightly branched polyethene. On the basis of an end-group analysis by FTIR and molecular weight analysis by GPC, we concluded that a chain transfer to ethene was the prevailing termination mechanism with Et[Ind]2ZrCl2/MAO at 80 °C in toluene. For the other catalyst systems, β-H elimination dominated at low ethene concentrations.

New bis(imino)pyridine-iron(II)- and cobalt(II)-based catalysts: synthesis, characterization and activity towards polymerization of ethylene

Abstract The synthesis of a new series of iron(II)- and cobalt(II)-based complexes of the general formula M(N∩N∩N)Cl 2 (M=Fe; M=Co) bearing 2,6-bis(imin)pyridyl ligands [A–NC–Py–CN–A] that carry bulky, alkyl-free aromatic terminals (A=naphthyl, pyrenyl, 2-benzylphenyl, phenyl) or chiral cycloaliphatic auxiliary moieties (A=((−)- cis -myrtanyl) is described. The Fe(II) complexes are exceptionally active (up to 40800 kg PE/(mol M h) towards the polymerization of ethylene in the presence of methylaluminoxane (MAO) as activator. Varying the steric bulkiness of the aromatic groups in the tridentate ligands affects catalytic productivity, molecular weight and for the first time the microstructure of the resulted material. The Fe(II) precatalysts are an order of magnitude more active than the corresponding Co(II) precatalysts.

Copolymerization of ethene with 1-hexene or 1-hexadecene over ethylene, dimethylsilylene and 1,4-butanediylsilylene bridged bis(indenyl) and bis(tetrahydroindenyl) zirconium dichlorides

Ethene was copolymerized with 1-hexene and 1-hexadecene over five different homogeneous methylaluminoxane (MAO) activated racemic ansa-metallocene catalysts in order to study both the influence of the ligand (indenyl and tetrahydroindenyl) and the influence of the interannular bridge (ethylene, dimethylsilylene and 1.4.-butanediylsilylene) on the copolymerization behaviour. Hydrogenation of the indenyl ligands was found to decrease comonomer content and molar mass of the copolymers. A similar tendency was observed for the ethylene bridge compared to the silylene bridges. The reasons for this behaviour are discussed and related to structural differences of the catalyst precursors. In addition a segregation fractionation technique was applied to study the chemical composition distribution (CCD) of the produced copolymers. Batchwise feed of comonomer resulted in a broad CCD. More homogeneous copolymers could be produced using partly continuous feed of comonomer.

Oxygen-Containing, Asymmetric “Dual-Side” Zirconocenes: Investigations on a Reversible Chain Transfer to Aluminum

A series of new oxygen-substituted, asymmetric zirconocene dichlorides (rac-{1-[5,6-(ethylenedioxy)-2-methyl-1-η5-indenyl]-2-(9-η5-fluorenyl)ethane}zirconium dichloride (3a), rac{1-[5,6-(ethylenedioxy)-2-methyl-1-η5-indenyl]-2-(9-η5-fluorenyl)ethane}dimethylzirconium (3b) and rac-{[5,6-ethylenedioxy)-2-methyl-1-η5-indenyl](9-η5-fluorenyl)dimethylsilane}zirconium dichloride (3c)} have been prepared and their polymerization behavior was investigated in dependence of monomer concentration, temperature and catalyst activation. The presence of oxygen substituents on the indenyl ring results in a strong increase of polymerization activities and also of polymer molecular weights with decreasing Al/Zr ratio. Significantly higher molecular masses and activities were found for the dimethyl complex 3b after activation with [(C6H5)3C+][(C6F5)4B−] deriving from the absence of chain transfer to aluminum and higher concentration of active catalyst species. The mechanism of stereoerror formation of the oxygen-containing C1-symmetric catalyst was investigated by deuterium labeling studies on propene monomers. The results are discussed on the basis of a reversible chain transfer to aluminum.

rac-[Ethylenebis(2-(thexyldimethylsiloxy)indenyl)]zirconium dichloride: Synthesis, molecular structure and olefin polymerization catalysis

Abstract The synthesis and molecular structure of rac -[ethylenebis(2-(thexyldimethylsiloxy)indenyl)]zirconium dichloride ( 4 ), is reported. In combination with methylaluminoxane (MAO), 4 forms an active catalyst system for homogeneous polymerization of ethylene and propylene. The high activity of 4 /MAO is retained at low [Al]:[Zr] ratios [(150–250):1]. Decreasing polymerization temperature or the [Al]:[Zr] ratio results in production of polyethylene having a high molecular weight shoulder in its molecular weight distribution (MWD). Deconvolution of the MWDs into a series of calculated Flory-distribution curves indicates that with this catalyst system ethylene is polymerized by three different types of active sites, whereas propylene is predominantly polymerized by two active sites. Complex 4 crystallizes in the indenyl-backward conformation. The ligand backbone adopts the expected C 2 symmetry.

Copolymerization of ethylene with 1-hexene or 1-hexadecene over siloxy-substituted metallocene catalysts

A series of ethylene copolymerizations with 1-hexene or 1-hexadecene over four different siloxy-substituted ansa-metallocene/methylaluminoxane (MAO) catalyst systems was studied. High copolymerization activities and comonomer responses were observed in all cases and high molecular weight ethylene copolymers were obtained. Unsaturations resulting from vinyl and vinylidene double bonds were observed in the produced copolymers. It can be concluded that the position of the siloxy substituent has a large influence on polymerization activity and that the replacement of the tert-butyldimethylsiloxy groups with triisopropylsiloxy groups increases copolymerization ability of the catalysts.

Long-Chain Branched Polyethene via Metallocene-Catalysis: Comparison of Catalysts

Metallocene catalysts have enabled the production of long-chain branched (LCB) polyethene at low pressure and temperature. The assumed LCB mechanism for the branched structure is the copolymerization of vinyl terminated macromonomers with ethene. In order to obtain LCB polyethene effectively, the employed metallocene-catalyst should be able to produce polyethene with vinyl terminals and effectively copolymerize the formed macromonomers with ethene. We present results of our recent investigation in which we have compared the properties of polyethenes polymerized with five conventional metallocene catalysts activated with methylaluminoxane (MAO); Et[Ind]2ZrCl2, Et[H4Ind]2ZrCl2, (n-BuCp)2ZrCl2, Me2Si[Ind]2ZrCl2 and Cp2ZrCl2. We have examined and discussed the relation between chain transfer mechanisms, hydrogen effect, copolymerization abilities, and rheological behavior of the polyethenes.

Synthesis and characterization of a silyl substituted bis(indenyl) zirconium dichloride and comparison of its olefin polymerization behavior to a siloxy substituted analogue

The synthesis and characterization ofrac-[ethylenebis(1-(tert-butyldimethy1silyl)-3-indenyl))zirconium dichloride (3) is reported. The silyl substituted 3/MAO was compared to its siloxy substituted analogue (4) in ethylene homo- and in ethylene-1-hexene copolymerizations to elucidate the effect of the heteroatom on polymerization performance. The influence of monomer and cocatalyst concentration and the polymerization temperature was investigated. The oxygen between the indenyl ligand and the bulky tert-butyldimethylsilyl group in the siloxy substituted 4/MAO was found to have a positive influence on polymerization activity and copolymerization performance.

Copolymerisation Properties of Siloxy-Substituted bis(Indenyl)zirconocene Catalysts: Modified Rheological Behaviour

The combination of the copolymerisation ability and vinyl end group selectivity of siloxy substitution of ethylene-bridged bis(indenyl) zirconium dichlorides suggest these catalyst as potential ones for the production of polyethylene containing small amounts of long chain branching. The role of the polymerisation conditions with these highly active catalysts can clearly be seen. Furthermore low contents of multiple branches may occur, even though the probability of attaching several macromonomers into one chain is low. The effect on melt rheological behaviour depends on both the amount of long chain branching and the length of the branch. Moreover the position of the siloxy group is very important. Polymers synthesized with catalysts, where the siloxy group is in position 1, give peculiar rheological behaviour resembling cross-linked networks although the polymers are completely soluble.