Copolymerization Of 1-hexene Research Articles

Effect of Catalysts Supporting on Tandem Polymerization of Ethylene Stock in Synthesis of Ethylene−1-Hexene Copolymer

Ethylene-1-hexene copolymers were synthesized with a tandem catalysis system consisting of a new trimerization catalyst (1), bis(2-dodecylsulfanylethyl)amine-CrCl3, and a copolymerization catalyst (2), Et(Ind) 2 ZrCl 2 . Catalysts 1 and 2 were supported on silica particles, and the effects of different supporting strategies on trimerization selectivity, 1-hexene incorporation efficiency, and copolymerization activity were studied and compared to the homogeneous system. It was found that the supported 1 trimerized ethylene with a similar selectivity (>99%) but one-quarter of the activity of the homogeneous 1. The supported 2 gave 40% 1-hexene incorporation efficiency and one-third of the copolymerization activity of the homogeneous 2. The tandem action of the supported 1 and 2 yielded linear low-density polyethylene (LLDPE) materials that contained only C4 side-chains. The dual supported system had activities at a 10 7 g/(mol Zr h) level, in the same order of the homogeneous counterpart. Adjusting the Cr/Zr ratio yielded various branching densities and, thus, melting temperatures of the resulting polymers. The samples prepared with the supported 2 exhibited broad differential scanning calorimetry (DSC) curves, probably due to multiple active sites.

Titanium-magnesium catalysts for olefin polymerization - effect of titanium oxidation state on catalyst performance

In this work, we investigated the influence of oxidation state of titanium and the effect of ethoxy groups' introduction into titanium compounds on the catalytic properties of MgCl2 - supported catalysts [with triisobutylaluminum (TIBA) or triethylaluminum (TEA) as cocatalyst] in ethylene polymerization and ethylene 1-hexene copolymerization, and on the polymer characteristics. To prepare supported titanium-magnesium catalysts of various compositions, soluble compounds of titanium in different oxidation states [?6-benzene-Ti2+Al2Cl8, Ti3+Cl3źnDBE, and Ti4+(OEt)2Cl2] were synthesized, analyzed by ESR and 13C NMR methods, and immobilized on the highly dispersed magnesium chloride. The data were obtained on the effects produced by composition and oxidation state of titanium compounds (covering also commonly used TiCl4) on the activity, control of PE molecular weight by hydrogen, copolymerization ability, and molecular weight distribution (MWD) of polyethylene. The results obtained demonstrate that different titanium precursors comprising Ti(II), Ti(III) and Ti(IV) compounds supported on MgCl2 allow preparing the highly active catalysts for ethylene polymerization or ethylene/1-hexene copolymerization. It was found that titanium oxidation state in the initial titanium compounds had a weak effect on the molecular weight and MWD of PE, whereas the ligand environment of titanium affected this parameter more strongly.

Entanglement network and relaxation temperature dependence of single‐site catalyzed ethylene/1‐hexene copolymers

AbstractIn this work, we investigate the linear viscoelastic response of high molecular weight ethylene/1‐hexene copolymers, characterized by a narrow molecular weight distribution and comonomer content in the range from 0 to 10 mol %. A variation in the entanglement plateau modulus has been found in agreement with the recently developed packing length model. The packing model applied to viscoelastic data suggests decreased values of the characteristic ratio, accordingly with recent computer simulation results. The flow activation energy increases as the side chain content increases. This feature is thought to be related to the mobility of the molecules. The presence of side branches due to the comonomer hinders the mobility of the molecules, and increases the thermal barrier for the segmental motion. Then in the comonomer content range studied, the increase of the flow activation energy goes parallel with a decrease in the characteristic ratio. This result suggests that more parameters than only the stiffness of the chain modulate the thermal dependence of viscoelastic properties. A more refined study is necessary combining experiments with computer simulations in order to elucidate these aspects. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

The Double Role of Comonomers on the Crystallization Behavior of Isotactic Polypropylene: Propylene−Hexene Copolymers

A study of the crystallization behavior of isotactic propylene−hexene copolymers prepared with metallocene catalysts is reported. These copolymers crystallize from the melt as mixtures of α and γ f...

Modeling and kinetics of tandem polymerization of ethylene catalyzed by bis(2-dodecylsulfanyl-ethyl)amine- [formula omitted] and [formula omitted

A mathematical model was developed to describe ethylene–1-hexene copolymerization with a tandem catalysis system. A series of semi-batch polymerization runs catalyzed by a trimerization catalyst bis(2-dodecylsulfanyl-ethyl)amine- CrCl 3 and a copolymerization catalyst Et ( Ind ) 2 ZrCl 2 in toluene at 74 ∘ C were carried out to verify the model. Both experimentation and modeling showed that adjusting the Cr/Zr ratio yielded various branching densities and thus melting temperatures, as well as molecular weights and polydispersities. Broad composition distributions and thus broad DSC curves were observed at high Cr/Zr ratios. Modeling results elucidated that this is due to an accumulation of 1-hexene component and to composition drifting during the copolymerization. It was also found that applying a short time period of pre-trimerization improved homogeneity in chain microstructure and minimized broadening in DSC curves.

DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Distribution of active centers (ACD) of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl2/TiCl4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components. Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducing α-olefin on ethylene polymerization. On the other hand, ACD of ethylene-1- hexene copolymer with very low ethylene incorporation was compared with that of 1-hexene homopolymer. Adding small amount of 1-hexene in ethylene polymerization caused marked activation of all the Flory components of the polymer, in which the low molecular weight components are activated more than the high molecular weight components. In 1-hexene polymerization system, the activity can also be greatly enhanced by introducing small amount of ethylene, but the different Flory components (or active centers) are activated with similar extent, except a newly emerged active center producing polymer with the lowest molecular weight. The total number of active centers is markedly increased by adding small amount of ethylene in 1-hexene polymerization, but the average catalysis efficiency of the active centers decreased. The broad composition distribution of the ethylene-1-hexene copolymer can be well understood from the ACD of catalyst and its dependence on the monomer.

Synthesis, Characterization, and Marked Polymerization Selectivity Characteristics of Binuclear Phenoxyiminato Organozirconium Catalysts

The new binuclear phenoxyiminato zirconium complex {1,7-(O)2C10H4-2,7-[CH=N(2,6-iPr2C6H3)]2}Zr2Cl6(THF)2 (FI2-Zr2) polymerizes ethylene with greater activity (approximately 8x) than the mononuclear analogue. Also, this catalyst produces high molecular weight ethylene + 1-hexene copolymers, while the mononuclear analogue yields only traces of copolymer under identical conditions. This ability to produce copolymers suggests cooperativity between the two Zr centers which promotes 1-hexene co-enchainment.

High molar mass ethene/1‐olefin copolymers synthesized with acenaphthyl substituted metallocene catalysts

AbstractThe influence of ligand structure on copolymerization properties of metallocene catalysts was elucidated with three C1‐symmetric methylalumoxane (MAO) activated zirconocene dichlorides, ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐cyclopentadienyl)ZrCl2 (1), ethylene(1‐(7, 9)‐diphenylcyclopenta‐[a]‐acenaphthadienyl‐2‐phenyl‐2‐fluorenyl)ZrCl2 (2), and ethylene(1‐(9)‐fluorenyl‐(R)1‐phenyl‐2‐(1‐indenyl)ZrCl2 (3). Polyethenes produced with 1/MAO had considerable, ca. 10% amount of trans‐vinylene end groups, resulting from the chain end isomerization prior to the chain termination. When ethene was copolymerized with 1‐hexene or 1‐hexadecene using 1/MAO, molar mass of the copolymers varied from high to moderate (531–116 kg/mol) depending on the comonomer feed. At 50% comonomer feed, ethene/1‐olefin copolymers with high hexene or hexadecene content (around 10%) were achievable. In the series of catalysts, polyethenes with highest molar mass, up to 985 kg/mol, were obtained with sterically most crowded 2/MAO, but the catalyst was only moderately active to copolymerize higher olefins. Catalyst 3/MAO produced polyethenes with extremely small amounts of trans‐vinylene end groups and relatively low molar mass 1‐hexene copolymers (from 157 to 38 kg/mol) with similar comonomer content as 1. These results indicate that the catalyst structure, which favors chain end isomerization, is also capable to produce high molar mass 1‐olefin copolymers with high comonomer content. In addition, an exceptionally strong synergetic effect of the comonomer on the polymerization activity was observed with catalyst 3/MAO. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 373–382, 2008

A Mathematical Model for the Kinetics of Crystallization in Crystaf

AbstractSummary: A series of ethylene homopolymers and ethylene/1‐hexene copolymers with different molecular weight distributions (MWD) and chemical composition distributions (CCD) was analyzed by crystallization analysis fractionation (Crystaf) at several cooling rates to investigate the effect of MWD, CCD, and cooling rate on their Crystaf profiles. Using these results, we developed a mathematical model for Crystaf that considers crystallization kinetic effects ignored in all previous Crystaf models and can fit our experimental profiles very well.

Characterization of Ethylene‐1‐Hexene Copolymers Made with Supported Metallocene Catalysts: Influence of Support Type

AbstractSummary: It is known that the nature of the support, as well as the technique used to anchor the metallocene onto it, play important roles on catalytic activity and on the properties of the polymers produced with supported metallocenes. In the present work, the effect of different support types on the microstructure of ethylene/1‐hexene copolymers made with supported metallocene catalysts has been investigated through the analysis of molecular weight and chemical composition distributions using high temperature gel permeation chromatography (GPC) and crystallization analysis fractionation (Crystaf). The copolymer samples obtained using commercial carriers (silica and silica‐alumina) had unimodal chemical composition distributions and were used to create a linear calibration curve relating the peak crystallization temperature from Crystaf and the comonomer content as determined by 13C NMR. This calibration curve is useful to determine the 1‐hexene fractions for each peak in the resins showing bimodal chemical composition distributions, such as those obtained with catalysts supported on MCM‐41 and SBA‐15 materials. The structure and chemistry of the support used had a large influence on comonomer incorporation and the shape of the chemical composition distribution of the polymer, which suggests that the supporting process creates different types of active sites.

Tailoring the Physical Properties of Isotactic Polypropylene through Incorporation of Comonomers and the Precise Control of Stereo- and Regioregularity by Metallocene Catalysts

Random copolymers of propylene with ethylene, butene, and hexene comonomers have been prepared with different metallocene catalysts. The used catalysts have allowed a precise control of concentration of stereodefects and high degree of comonomer incorporation while maintaining high molecular mass and random distribution of comonomers. Incorporation of ethylene, butene, and hexene produces great enhancement of ductility, flexibility, and toughness, as compared to highly isotactic polypropylene, but with important differences in the values of elastic modulus and strength depending on the comonomer. In propylene−ethylene copolymers, the values of elastic modulus, ductility, toughness, and strength can be tuned by changing the concentrations of rr stereodefects and ethylene units, so that stiff and fragile plastics, highly flexible materials, and elastomers can be obtained. Propylene−butene copolymers behave as highly flexible materials with remarkable ductility and toughness and contemporary high strength and stiffness. Propylene−hexene copolymers are highly flexible materials with plastic resistance and strength that decrease with increasing hexene content. These outstanding properties are not easily accessible with propylene-based copolymers produced with traditional Ziegler−Natta catalysts because of nonrandom distribution of comonomers and non-homogeneous composition.

Analysis of polyolefins and olefin copolymers using Crystaf technique: Resolution of Crystaf curves

AbstractAn experimental technique, crystallization analysis fractionation (Crystaf), is used to analyze compositional uniformity of ethylene/α‐olefin copolymers and isotactic polypropylene. A computerized method for quantifying Crystaf data is developed based on resolution of Crystaf curves into their elemental components, with each component representing a fraction of the polymer with the same degree of chain imperfection. This analysis of Crystaf curves gives three parameters characterizing crystallizable polymer material: (a) the number of compositionally uniform components, (b) properties of each compositionally uniform component (in the case of ethylene/α‐olefin copolymers, the comonomer content), and (c) the quantity of each component. Crystaf analysis of several ethylene/1‐hexene copolymers produced with supported Ti‐based Ziegler‐Natta catalysts shows the existence of two groups of copolymer components. The first group includes components with low comonomer content, in the Crystaf analysis they precipitate at high temperatures as several relatively sharp peaks. The second group includes components with high comonomer contents; they precipitate at much lower temperatures, as a broad overlapping group of peaks. The peak resolution technique was applied to analysis of ethylene/α‐olefin copolymers prepared with a supported catalyst at different temperatures, a copolymer produced with a pseudo‐homogenous Ziegler‐Natta catalyst, and to isotactic polypropylene. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

Mathematical modeling of crystallization analysis fractionation of ethylene/1‐hexene copolymers

AbstractCrystallization analysis fractionation (Crystaf) is a polymer characterization technique for estimating the chemical composition distributions of semicrystalline copolymers. Although Crystaf has been widely used during the recent years, it is still a relatively new polymer characterization technique. More quantitative understanding of its fractionation mechanism is essential for further developments. In this work, three ethylene/1‐hexene copolymers with different 1‐hexene fractions, but similar number‐average molecular weights, were analyzed by Crystaf at several cooling rates. A mathematical model was proposed to describe the effect of comonomer fraction and cooling rate on Crystaf fractionation from a fundamental point of view. The model describes the experimental Crystaf profiles of ethylene/1‐hexene copolymers with different 1‐hexene fractions measured at distinct cooling rates very well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1010–1017, 2007

Cationic scandium aminobenzyl complexes. Synthesis, structure and unprecedented catalysis of copolymerization of 1-hexene and dicyclopentadiene

A structurally well-defined THF-free cationic half-sandwich scandium aminobenzyl complex serves as a novel catalyst for the first copolymerization of 1-hexene with dicyclopentadiene to give the random copolymers with a wide range of 1-hexene contents (32-70 mol%) unavailable previously.

Effect of methylaluminoxane/transition-metal ratio on the physical properties and chemical composition distributions of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst

A silica–magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for the impregnation of TiCl 4 and rac-Et(Ind) 2ZrCl 2. The prepared rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO(methylaluminoxane)/SMB catalyst was applied to the ethylene–hexene copolymerization under the conditions of variable Al(MAO)/Zr ratio and fixed Al(TEA, triethylaluminum)/Ti ratio. The effect of Al(MAO)/Zr ratio on the physical properties and chemical composition distributions of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst was investigated. The catalytic activity of rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB was steadily increased with increasing Al(MAO)/Zr ratio from 200 to 500. The ethylene–hexene copolymer produced with Al(MAO)/Zr = 300, 400, and 500 showed two melting points at around 110 °C and 130 °C, while that produced with Al(MAO)/Zr = 200 showed one melting point at 136 °C. The number of chemical composition distribution (CCD) peaks was increased from 4 to 7 and the short chain branches of ethylene–hexene copolymer were distributed over lower temperature region with increasing Al(MAO)/Zr ratio. The lamellas in the copolymer were distributed over lower temperature region and the small lamellas in the copolymer were increased with increasing Al(MAO)/Zr ratio. The rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst preferably produced a ethylene–hexene copolymer with non-blocky sequence ([EHE]) with increasing Al(MAO)/Zr ratio.

Chemical composition distributions and microstructures of ethylene–hexene copolymers produced by a rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for a metallocene/Ziegler–Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl 4 and rac-Et(Ind) 2ZrCl 2. The prepared rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB catalyst was applied to the ethylene–hexene copolymerization with variable amounts of 1-hexene used. The catalytic activity of rac-Et(Ind) 2ZrCl 2/TiCl 4/MAO/SMB showed a volcano feature with respect to the amount of comonomer used. The melting point attributed to the Ziegler–Natta catalyst was not changed significantly, while that attributed to the metallocene catalyst was broadened and gradually shifted to the lower temperature with increasing 1-hexene content. The number of chemical composition distribution (CCD) peaks was increased and the short chain branches were distributed over the lower temperature region with increasing 1-hexene content. The majorities of lamella distributions whose content was more than 50 wt.% shifted to the smaller lamella size with increasing 1-hexene content. The average sequence length of ethylene was steadily decreased with increasing comonomer content, while that of 1-hexene was not changed significantly. Both blocky sequence ([EHH]) and non-blocky sequence ([EHE]) were increased with increasing comonomer content. However, the increasing rate of blocky sequence formation was much higher than that of non-blocky sequence.

(Co)polymerisation Behaviour of Supported Metallocene Catalysts: Carrier Effect

AbstractSummary: The polymerisation and copolymerisation of ethylene with 1‐hexene over metallocene catalysts L2ZrCl2/MAO (L = Cp, n‐BuCp, t‐BuCp, i‐PrCp, Me5Cp) supported on different types of carriers (MgCl2(MeOH)6 or silica with CH3 surface groups obtained in the sol‐gel process) were studied. It was demonstrated that both the metallocene structure and the type of inorganic support affected catalyst activity and polymer properties such as melting point, molecular weight and molecular weight distribution. The metallocene structure also determined comonomer incorporation, both for homogeneous and supported catalytic systems. When a catalyst is anchored on a support, it becomes less effective at incorporating a comonomer into the polyethylene chain, and the type of the support material has no influence on that process. The type of carrier used does, however, have an influence on the molecular weight and molecular weight distribution of the product obtained. Most polymers and copolymers obtained with catalysts supported on an oxide carrier have higher molecular weights and broader molecular weight distributions than those produced by catalysts anchored on a magnesium compound.Melting curves (obtained using the SSA method) of ethylene/1‐hexene copolymers synthesised with Cp2ZrCl2/MAO (A) and with the same catalyst supported on various carriers (B,C,D).magnified imageMelting curves (obtained using the SSA method) of ethylene/1‐hexene copolymers synthesised with Cp2ZrCl2/MAO (A) and with the same catalyst supported on various carriers (B,C,D).

Crystal Structure of Isotactic Propylene−Hexene Copolymers: The Trigonal Form of Isotactic Polypropylene

A study of the structure of isotactic propylene−hexene random copolymers, prepared with single-center metallocene catalysts, is reported. For low concentrations of hexene comonomeric units, up to nearly 10 mol %, copolymers crystallize in the α form of isotactic polypropylene. Copolymers with hexene contents higher than 10 mol % crystallize in a new polymorphic form that melts at nearly 50 °C. The hexene units are partially included in both crystals of α form and of the new form. The crystallization of the new crystalline form allows incorporation of a high amount of hexene units. The melting temperature and the crystallinity decrease rapidly with increasing hexene content. A slower decrease of melting temperature and crystallinity is observed at high hexene concentrations because of the crystallization of the new form. The crystal structure of the new form has been studied by analysis of X-ray powder and fiber diffraction patterns of samples containing hexene concentration higher than 10 mol %. Chains in 3-fold helical conformation of propylene−hexene copolymers are packed in a trigonal unit cell according to the space group R3c or R3̄c. The values of a and b axes of the unit cell depend on hexene concentration, and values of a = b = 17.5 Å and c = 6.5 Å have been found for the sample with 26 mol % of hexene. The structure contains high degree of disorder due to the constitutional disorder of the random copolymer chains that produces disorder in the positioning of the lateral groups in the unit cell. Moreover, statistical disorder in the up−down positioning of the helical chains and slight disorder in the orientation of chains around the 3-fold axes are present. The inclusion of hexene units in the crystals induces a suitable increase of density that allows crystallization of 3-fold helical chains in the trigonal form, where the helical symmetry of the chains is maintained in the crystal lattice. The structure is similar to that of form I of isotactic polybutene. This form does not crystallize, and has never been observed so far for the polypropylene homopolymer because, in the absence of bulky side groups, it would have a too low density. This structure represents an example of entropy-driven phase formation.

A Structure of Copolymers of Propene and Hexene Isomorphous to Isotactic Poly(1-butene) Form I

Isotactic copolymers of 1-propene and 1-hexene that contain over 10% and up to about 25% of hexane units in the chain have been shown to crystallize in an unusual crystal modification that differs significantly from the well-known structures of isotactic polypropylene (α, β, and γ phases) or of isotactic poly(1-hexene) (Macromolecules 2005, 38, 1232). The experimental data obtained by Poon et al. are reinterpreted and analyzed. The new crystal form has a trigonal unit-cell with parameters a = b = 1.717 nm, c = 0.65 nm, very similar to form I of isotactic poly(1-butene) (iPBu) (trigonal cell with parameters a = b = 1.770 nm, c = 0.65 nm). The chain conformation is the 3-fold helix of isotactic polypropylene. The side-chain material in the copolymer with the highest hexene content (25%) is about 12% less than in iPBu form I (all ethyl units). These copolymers of propene and hexene adopt a crystal structure isomorphous to that of a third polyolefin (polybutene) that, in terms of overall composition, is close to the average of the two “parent” olefins.

Physical property and chemical composition distribution of ethylene–hexene copolymer produced by metallocene/Ziegler–Natta hybrid catalyst

Silica–magnesium bisupport (SMB) was prepared by a sol–gel method for use as a support for metallocene and metallocene/Ziegler–Natta hybrid catalysts. SMB was treated with methylaluminoxane (MAO) prior to catalyst immobilization. The supported heterogeneous catalysts were applied to the ethylene copolymerization with 1-hexene. The h-copolymer (ethylene–hexene copolymer produced by metallocene/Ziegler–Natta hybrid catalyst) showed two melting points and broad molecular weight distribution. The differences in physical properties between h-copolymer and m-copolymer (ethylene–hexene copolymer produced by metallocene catalyst) could be explained by the differences in chemical composition and side chain distributions of the produced copolymers.