Anneli Malmberg

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.

The production of ethene/propene/5‐ethylidene‐2‐norbornene terpolymers using metallocene catalysts: Polymerization, characterization and properties of the metallocene EPDM

Metallocene catalysts Et(Ind)2ZrCl2/MAO and Et(Ind)2HfCl2/MAO were used in ethene/propene copolymerization and in ethene/propene/5-ethylidene-2-norbornene (E/P/ENB) terpolymerization. The copolymerization activity of the Et(Ind)2ZrCl2/MAO system was 20 × 103 kgpolym/molMt *h, the Et(Ind)2HfCl2/MAO yielding 5 × 103 kgpolym/molMt *h. The polymerization activity decreased with diene addition, but this effect was significant only at very large diene feeds. The catalysts incorporated diene readily. Materials with an ethene content of 55 to 70 mol % and an ENB content of 2 to 16 mol % were produced. Et(Ind)2HfCl2 produced a considerably higher molar mass material than the Et(Ind)2ZrCl2 catalyst. The molar mass distributions were narrow. Copolymers and terpolymers with up to 3 mol % ENB content had some crystallinity. Copolymer Tgs were between −59°C and −55°C. The terpolymer glass transition temperature rose 1.5°C per wt % of ENB in the polymer. Polymer characteristics reported include composition, molar mass distribution, melt flow rate, density, and thermal behavior. The dynamic mechanical and rheological properties of the materials in comparison with commercial E/P/ENB terpolymers are discussed.

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.

Studies on Properties of Metallocene Catalysed Copolymers of Ethylene and Linear, Non-conjugated Dienes

The effect of diene addition on the structure of ethylene copolymer was studied. The dienes used were 1,5-hexadiene (HD), 1,7-octadiene (OD), and 7-methyl-l,6-octadiene (MOD).Polymerizations were conducted in n-heptane in the presence of the metallocene catalyst cyclopentadienyl zirconium dichloride (Cp2ZrCl2) with methylaluminoxane (MAO) as a cocatalyst. The structure of the copolymer was determined by NMR-techniques. The 1,5-hexadiene comonomer was predominantly incorporated as a 5 member ring structure into the polyethylene backbone. OD and MOD formed branches in the polyethylene chain. The ethylene/HD copolymers were analysed using dynamic rheometry to study the effect of ring structures on the rheological properties of the product. The ring structures stiffen the chain, which was manifested as increasing viscosity and shear sensitivity of the melt. At low hexadiene ring content, the effect of the ring structure was masked by the long chain branching already present in the ethylene homopolymer.

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.