Barbro Löfgren

Polymerization of ethylene with new diimine complexes of late transition metals

Three pyridylimine based complexes of NiII and CoII were reacted with methylaluminoxane (MAO) and tested as catalysts in ethylene polymerization. The two nickel catalysts produced mainly methyl branched polymers with good to moderate activity, while the cobalt compound showed only marginal activity. Reaction conditions strongly affect the polymer properties, such as molecular weight, melting temperature, degree of branching, and chain end unsaturation type.

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.

Functionalization of polyethylenes via metallocene/methylaluminoxane catalyst

Abstract Ethylene was copolymerized with 1,1-dimethyl-2-propen-1-ol, 5-hexen-1-ol, 10-undecen-1-ol, methyl-9-decenoate and 10-undecenoic acid in the presence of the catalyst system ( n -BuCp) 2 ZrCl 2 /MAO. The addition of a polar comonomer resulted in a rapid deactivation of the catalyst, which was mainly due to the interactions between polar comonomer and Lewis acid catalyst components. A comparison between 5-hexen-1-ol and 10-undecen-1-ol revealed that the increase in the number of carbon atoms between the functional group and double bond did not influence the polymerization rate decreasing effect of the polar comonomer, but increased its incorporation to the copolymer. Steric hindrance in the vicinity of the hydroxyl group hindered the 1,1-dimethyl-2-propen-1-ol from reacting with the catalyst components but, on the other hand, the steric protection made the comonomer unable to copolymerize. Compared with 10-undecen-1-ol, methyl-9-decenoate and 10-undecenoic acid showed lower reactivities in the polymerizations. The GPC profiles of the samples showed a reduction in the molar masses and a marked broadening in the molar mass distributions of the polymers with the addition of the polar comonomer indicating the presence of multiple active sites in the catalyst.

Thermal properties of ethylene/long chain α-olefin copolymers produced by metallocenes

Metallocene type copolymers of ethylene with the α-olefins 1-octene, 1-tetradecene and 1-octadecene were characterized by dynamic scanning calorimeter (DSC) and by dynamic mechanical analysis (DMA). At a similar comonomer content above 3 mol%, the higher α-olefins gave lower melting points, crystallinities and densities than 1-octene. In DSC a separation technique sorting the crystalline sequence lengths of the polymer into groups was applied, and DSC index, DI, which gave a semiquantitative idea of the chemical homogeneity of the comonomer compositional distributions. By DMA the storage modulus as an indicator of stiffness and loss modulus and loss tangent as a measure of the effect of branching on the β relaxations were studied. The DMA measurements showed the loss modulus maximum to be a more sensitive value than the loss tangent maximum for the characterization of the comonomer distribution. The intensity of the β transition of 1-octadecene did not increase with increasing branching in contrast to the situation for 1-octene and 1-tetradecene copolymers.

Metallocene/methylaluminoxane-catalyzed copolymerizations of oxygen-functionalized long-chain olefins with ethylene

Copolymerizations of ethylene with 10-undecen-1-ol, 10-undecenyl methyl ether, 10-undecenyl trimethyl silyl ether, and 1-undecene were performed with rac-ethylene-bis(1-indenyl)zirconium dichloride as a catalyst and methylaluminoxane as a cocatalyst. All three oxygen-functional comonomers copolymerized with ethylene, although the activity of the catalyst decreased considerably compared with the homopolymerization of ethylene. The conversions of the comonomers varied from 17 to 40%, depending on the amount of comonomer in the feed. Under the same conditions, the conversion of 1-undecene was 50–75%. The incorporation (0.7–3.6 mol %, depending on the feed) and the effect on the activity of the catalyst were on the same level for all the functional comonomers, which indicates that trimethylsilyl or methyl groups do not act as effective protecting groups for oxygen atoms. According to NMR and Fourier transform infrared analyses, the final functional group in the copolymers of the trimethylsilyl ether comonomer was hydroxyl. In contrast, the methyl ether group remained untouched in the copolymer, which suggests that the formation of aluminum alkoxides via a reaction with a cocatalyst is not a prerequisite for comonomer incorporation.

Co- and terpolymerizations of ethene and α-olefins with metallocenes

The suitability of the (n-butCp) 2 ZrCl 2 /methylaluminoxane (MAO) catalyst system for the copolymerization of ethene with propene, hexene, and hexadecene was studied and Ind 2 ZrCl 2 /MAO was tested as a catalyst for ethene/propene and ethene/hexene copolymerizations. The synergistic effect of longer α-olefin on propene incorporation in ethene/ propene/hexene and ethene/propene/hexadecene terpolymerizations was investigated with Et(Ind) 2 ZrCl 2 /MAO and (n-butCp) 2 ZrCl 2 /MAO catalyst systems. The molar masses, molar mass distributions, melting points, and densities of the products were measured. The incorporation of comonomer in the chain was further studied by segregation fractionation techniques (SFT), by differential scanning calorimetry (DSC), studying the β relaxations by dynamic mechanical analysis (DMA) and by studying the microstructure of some copolymers by 13 C-NMR. In this study (n-butCp) 2 ZrCl 2 and Ind 2 ZrCl 2 exhibited equal response in copolymerization of ethene and propene and both catalysts were more active towards propene than longer α-olefins. A nearly identical incorporation of propene in the chain was found for the two catalysts when a higher propene feed was used. A lower hexene feed gave a more homogeneous comonomer distribution curve than a higher hexene feed and also showed the presence of branching. In terpolymerizations catalyzed with (n-butCp) 2 ZrCl 2 , the hexadecene concentrations of the ethene/propene/hexadecene terpolymers were always very low, and only traces of hexene were detected in ethene/propene/hexene terpolymers. With hexene no clear synergistic effect on the propene incorporation in the terpolymer was detected and with hexadecene the effect of the longer a-olefin was even slightly negative. With an Et(Ind) 2 ZrCl 2 /MAO catalyst system both hexene and hexadecene were incorporated in the chain in the terpolymerizations.

A comparison of (n-butCp)2ZrCl2 and other simple metallocenes with bridged Et(Ind)2ZrCl2 and Me2Si(Ind)2ZrCl2 catalysts in ethene/propene copolymerization

Abstract A study was made of the behaviour of four non-bridged metallocenes, in particular (n-butCp)2ZrCl2 in ethene/propene (E/P) copolymerization, and the findings were compared with those for bridged Et(Ind)2ZrCl2 and Me2Si(Ind)2ZrCl2 catalysts. Methylaluminoxane was used as a cocatalyst in all polymerizations. The influence of the catalyst structure on the propene content, the reactivity ratios, the comonomer distribution in the polymer backbone, molar mass, molar mass distribution, density and melting point of the synthesized material were of interest. The bridged metallocenes were found to be more active catalysts for propene incorporation than the non-bridged ones. The comonomer distributions of all polymers except those obtained with an Ind2ZrCl2 catalyst were random. At the same propene molar content in the copolymer, densities and melting points were lower for materials synthesized with non-bridged catalysts than for materials synthesized with bridged catalysts due to the lack of chirality in the catalysts of C2v symmetry. Except Cp2ZrCl2, the non-bridged metallocenes produced higher molar mass copolymers than their bridged analogues. Polydispersities of the materials varied with the catalyst and no uniformity of behaviour was detected for the simple metallocenes.

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.

NMR studies on the reactivity of aluminium compounds with an unsaturated alcohol

The interaction of an unsaturated alcohol, 10-undecen-1-ol (CH2  CH(CH2)8CH2OH), with aluminium compounds AlEt3 and MAO (30% toluene solution) has been studied. The reactions were investigated at room and elevated temperatures and followed by 1H, 13C and 27Al NMR-spectroscopy. The alcohol end group of 10-undecen-1-ol reacts quantitatively with aluminium alkyls (AlEt3 as well as AlMe3 present in MAO), liberating alkane gas and forming in the first step the dimeric complexes [R′2AlOR]2 and [R′Al(OR)2]2 (R′ = Me, Et; R = 10-undecen). In the presence of excess 10-undecen-1-ol the alkyl aluminium alkoxides are found to generate tetrameric aluminium compounds, Al4(R′)n(OR)12−n (n = 6,4) containing six-coordinated central aluminium surrounded by six oxygen atoms. The structural assignment is based on 13C as well as 27Al NMR, where narrow resonances at 8.21 and 7.3 ppm are observed for Al4Me6(OR)6 and Al4Et6(OR)6, respectively. Besides the above reaction between the alcohol moiety and AlR3 another effect was also visible in the reaction of 10-undecen-1-ol with MAO. Broad carbon resonances were observed in 13C NMR at the downfield side of the normal olefinic and alkoxy carbon resonances, indicating some kind of interaction of methylaluminoxane with the corresponding carbon atoms.