Esa Kokko

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.

Analytical and rheological characterization of long-chain branched metallocene-catalyzed ethylene homopolymers

Abstract The aim of this paper is to compare the results of analytical and rheological characterization techniques with respect to the analysis of long-chain branches (LCB) in polyethylenes. The materials investigated are metallocene-catalyzed ethylene homopolymers into which LCB were introduced by the selection of appropriate polymerization conditions. The samples were characterized analytically by 13C NMR, IR-spectroscopy, and size exclusion chromatography coupled with a multi-angle laser light scattering detector. The rheological characterization was performed using dynamic–mechanical measurements and creep and creep recovery experiments in shear. It was found that the analytical methods were in good qualitative agreement for the most highly branched sample whose LCB content was 0.12 LCB/1000 C as determined by 13C NMR spectroscopy. However, even a 10-times lower LCB content, which is almost beyond the detection limit of 13C NMR measurements, had a significant impact on the rheological behavior. Rheological experiments clearly indicated the presence of LCB by changes in the frequency dependence of dynamic–mechanical material functions and the molecular mass dependence of the zero shear-rate viscosity in comparison to linear polyethylenes.

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.

Functional Polyolefins Through Polymerizations by Using Bis(indenyl) Zirconium Catalysts

The discovery of metallocene catalysts has enabled synthesis of new polyolefin structures through the ability to incorporate comonomers that are not applicable using Ziegler–Natta or other conventional olefin polymerization catalysts. Extensive research has been carried out on the copolymerization behavior of different bis(indenyl) zirconium catalysts in order to understand their comonomer response, chain termination mechanisms, and chain-end isomerization. Metallocene-catalyzed copolymerization enables unforeseen material structures, leading to functional polyolefins with strongly or weakly interacting comonomers or long-chain branches. These copolymers show interesting technical properties like reactive functionality, compatibility, adhesion properties, and modified rheology.

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.