Supported Ziegler-Natta Catalysts Research Articles

DRIFTS study of the interaction of the AlEt 3 cocatalyst with the internal donor ethyl benzoate in supported Ziegler–Natta catalysts

The interaction of AlEt 3 cocatalyst with the internal donor (ethyl benzoate–EB) in the supported Ziegler–Natta (TiCl 4/EB/MgCl 2) catalysts and the EB/MgCl 2 support was studied by DRIFT spectroscopy. For EB/MgCl 2 samples, it was shown that AlEt 3 firstly removed the more weak surface complexes of EB from the MgCl 2 surface and competed with EB at adsorbtion for releasing sites of the MgCl 2 surface. EB, as the external donor, keeps constant the initial content and distribution of surface complexes of EB at the interaction of the AlEt 3/EB mixture with the EB/MgCl 2 support. At the interaction of AlEt 3 with the TiCl 4/EB/MgCl 2 catalysts one type of surface complexes of EB is mainly removed. A part of removed EB adsorbs again on the catalyst surface in the form of complexes with aluminum-containing compounds. At the interaction of the catalyst with the AlEt 3/EB mixture the EB content in the catalyst changes slightly, but the distribution of different surface complexes of EB in the catalyst changes noticeably compared to that in the initial catalyst. EB, as the external donor, adsorbs both on surface MgCl 2 sites released at the removal of the internal donor and on aluminum-containing compounds adsorbed on the catalyst surface.

Immobilized organometallic catalysts in the catalytic polymerization of olefins

Studies in the field of supported Ziegler-Natta catalysts employed for the polymerization of olefins that were begun by works performed under the guidance of Prof. Chirkov are reviewed in brief. The development of immobilization procedure for metallocene catalysts including the synthesis of alkylaluminoxanes heterogenized on the support surface via the partial hydrolysis of AlR3 by water contained in the support and subsequent supporting of a metallocene is described. It is revealed how the immobilization of various metallocenes on the solid surface affects the activity of the catalysts and the structure and molecular mass of the polymers. The use of immobilized organometallic catalysts for the polymerization filling of polyolefin matrices aimed at the design of new polymer composites with special characteristics and preparation of polyolefin nanocomposites is considered.

Nanoporous structure of ultrahigh-molecular-weight polyethylene reactor powder

The influence of the catalyst system and synthesis conditions on the morphology and molecular dynamics of reactor (nascent) powders of ultrahigh-molecular-weight PE synthesized over supported Ziegler-Natta catalysts in laboratory reactors was studied by means of electron microscopy and 1H broadline NMR spectroscopy. For comparison, commercial reactor powders were studied as well. The type of the catalyst system and the temperature of slurry polymerization have a substantial effect on the supermolecular structure of the nascent polymer. The proton NMR spectra of the reactor powders synthesized at low temperatures display a narrow component. An analysis of its behavior at low temperatures and different humidities led to the conclusion that the signal is due to water localized in nanopores of 2–4 nm in size in the nascent polymer. The role of nanopores in the sintering of reactor particles is discussed.

Theoretical investigation of (MgCl2)xpolynuclear species formed during preparation of MgCl2-supported Ziegler–Natta catalysts from solid solvates

A novel approach for the study of the nature of the active species in Ziegler–Natta catalysis is described. This approach is based on the study of reliable structural models for disordered (MgCl2)xpolynuclear species which develop during the preparation of MgCl2-supported catalysts starting from MgCl2–Lewis-base adducts, and the calculation of X-ray diffraction patterns of these models. A method for the calculation of the X-ray powder diffraction patterns of the model structures is devised. This diffraction modelling method may be useful for the correct interpretation of the nature of some diffraction features in the X-ray diffraction patterns recorded during the structural evolution of MgCl2–Lewis-base adducts, which occurs in the preparation of the catalyst systems used for Ziegler–Natta polymerization of olefins.

SUPPORTED ZIEGLER-NATTA CATALYSTS FOR ETHYLENE SLURRY POLYMERIZATION AND CONTROL OF MOLECULAR WEIGHT DISTRIBUTION OF POLYETHYLENE

The effect of chemical composition of highly active supported Ziegler-Natta catalysts with controlled morphology on the MWD of PE has been studied. It was shown the variation of transition metal compound in the MgCl2-supported catalyst affect of MWD of PE produced in broad range: Vanadium-magnesium catalyst (VMC) produce PE with broad and bimodal MWD (Mw/Mn = 14−21). MWD of PE, produced over titanium-magnesium catalyst (TMC) is narrow or medium depending on Ti content in the catalyst (Mw/Mn = 3.1−4.8). The oxidation state of the initial titanium compounds in TMC has only slight effect on MWD of PE produced. Based on MWD data of PE heterogeneity of active centers of TMC and VMC was studied. The results of resolution of experimental GPC curves into Flory components indicated three Flory components are sufficient to describe MWD curve of PE, produced with TMC; six Flory components are required in the case of VMC. In the case of copolymerization of ethylene with 1-hexene over TMC the addition of 1-hexene leads to decrease of MW and to slight effect on Mw/Mn values. On the contrary the strong effect of 1-hexene on MWD of PE produced over VMC was found: the introduction of 1-hexene results in considerable broadening of MWD due to the shifting of the main MWD peak to low MW region. At that comonomer doesn't affect the position of high molecular weight shoulder. The results indicate that some of active centers of VMC producing high MW polymer are not active in the reaction of chain transfer with comonomer.

POISONING OF ACTIVE SITES ON ZIEGLER-NATTA CATALYST FOR PROPYLENE POLYMERIZATION

The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated. A minor amount of simple structure of Lewis base, i.e., methanol, acetone, ethyl acetate, was introduced into the catalyst slurry for partial poisoning catalytic active centers. It was found that the variations in deactivation power were in the order of methanol > acetone > ethyl acetate. The kinetic investigation via stopped-flow polymerization showed that poisoning compounds caused a decrease in activity through the reduction of the number of active sites whereas no effect on the degree of isotacticity was observed.

Formation of (MgCl2)x Polynuclear Species During Preparation of Active MgCl2 Supported Ziegler–Natta Catalysts from Solid Solvates with Lewis Bases

During the structural evolution of MgCl2 Lewis base adducts for the industrial preparation of heterogeneous Ziegler–Natta catalysts, disordered polynuclear (MgCl2)x species are formed that explain the high degree of nanoporosity of the active δ form of MgCl2 obtained in the process.

In-reactor stabilization of polypropene

Propene was polymerized with a high activity, high stereospecific supported Ziegler–Natta catalyst in presence of phenolic antioxidants (AO), phosphite processing stabilizers (PS) or sterically hindered amine stabilizers (HAS). PS and some HAS grades did not influence propene polymerization, but AO and most commercial HAS could interfere with the catalyst and reduce catalyst activity.

Kinetic features of ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

AbstractThe effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl2/MgCl2‐Al(i‐Bu)3 (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl2/MgCl2‐Al(i‐Bu)3 has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl2/MgCl2‐Al(i‐Bu)3 has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007

Effect of silica-type sol–gel carrier’s structure and morphology on a supported Ziegler–Natta catalyst for ethylene polymerization

Silica xerogels with different structures and morphology, synthesized using a sol–gel procedure, were used as a carrier of vanadium catalysts (VOCl 3/AlEt 2Cl) for ethylene polymerization. Two techniques of catalyst synthesis were applied: slurry impregnation and gas-phase adsorption and the relevant polymerization methods were then employed. The effect of the carrier structure and morphology on the vanadium loading in the catalysts, the catalyst’s activity and kinetic stability were investigated.

High temperature polymerization of propylene catalyzed by MgCl2‐supported Ziegler–Natta catalyst with various cocatalysts

AbstractFour cocatalysts, referred to as ethylaluminoxanes, were synthesized by the reaction between triethylaluminium (AIEt3) and water under various molar ratios of H2O/Al at −78°C. Aluminoxanes were used as cocatalysts for a MgCl2‐supported Ziegler–Natta catalyst for propylene polymerization at temperatures ranging from 70 to 100°C. When the polymerization was activated by AlEt3, the activity as well as the molecular weight and isotacticity of the resulting polymer gradually dropped as the temperature varied from 70 to 100°C. When ethylaluminoxane was employed as the cocatalyst, good activity and high molecular weight and isotacticity were obtained at 100°C. Furthermore, when the cocatalyst varied from AlEt3 to ethylaluminoxane, the atactic fraction and polymer fraction with moderate isotacticity decreased and the high isotactic fraction slightly increased, which indicated that the variation of the cocatalyst significantly affects the isospecificity of active sites. It was suggested that the reactivity of the Al‐Et group and the size of the cocatalyst were correlated to the performance of the Ziegler–Natta catalyst at different temperatures. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1978–1982, 2006

XPS characterization of supported Ziegler–Natta catalysts

Surface analytical technique ESCA (electron spectrometer for chemical analysis) has been used for analysis of catalysts used in propylene polymerization. As a result of this analysis it has been shown that productivity of a catalyst can be correlated to Ti/Mg atomic ratio that indicates dispersion of titanium atoms on magnesium support. A quantitative indicator of productivity, i.e. “titanium index” has also been evaluated for studied catalysts.

Ethylene polymerization using a novel MgCl2/SiO2‐supported Ziegler–Natta catalyst

AbstractA novel MgCl2/SiO2‐supported Ziegler–Natta catalyst was prepared using a new one‐pot ball milling method. Using this catalyst, polyethylenes with different molecular weight distributions were synthesized. The effects of the [Si]/[Mg] ratio, polymerization temperature and [Al]/[Ti] ratio on the catalytic activity, the kinetic behaviour and the molecular weight and the polydispersity of the resultant polymer were studied. It was found that the polydispersity index of the polymer could be adjusted over a wide range of 5–30 through regulating the [Si]/[Mg] ratio and polymerization temperature, and especially when the [Si]/[Mg] ratio was 1.70, the polydispersity index could reach over 25. This novel bi‐supported Ziegler–Natta catalyst is thus useful for preparing polyethylene with a required molecular weight distribution using current equipment and technological processes. Copyright © 2005 Society of Chemical Industry

DRIFT study of internal donors in supported Ziegler–Natta catalysts

The state of internal donor (ID) in the supported titanium–magnesium (TiCl 4/ID/MgCl 2) catalysts for stereospecific propylene polymerization has been studied by diffuse reflectance infrared spectroscopy (DRIFT). The samples were prepared via interaction of highly dispersed MgCl 2 with different IDs (ethyl benzoate, EB; di- n-butyl phthalate, DBP) and TiCl 4. It was found that the DRIFT spectra of carbonyl groups of IDs adsorbed on MgCl 2 could be best described as a superposition of several overlapping vibration bands from a variety of surface complexes. Within this model the content of individual EB and DBP complexes on the MgCl 2 surface was calculated. In the case of EB, three main complexes were found on the MgCl 2 support in about equal proportions. In the case of DBP, only one of three complexes was preferentially formed. The surface content of both EB and DBP was found to decrease in presence of TiCl 4. At the same time TiCl 4 had influenced the distribution pattern of EB but not DBP complexes. The most likely scenario of competitive adsorption of TiCl 4 and IDs on the MgCl 2 support is discussed. A model describing surface distribution of TiCl 4 on MgCl 2 is proposed for TiCl 4/EB/MgCl 2 and TiCl 4/DBP/MgCl 2 catalysts.

Effect of diether as internal donor on MgCl2‐supported Ziegler–Natta catalyst for propylene polymerization

AbstractThis article demonstrates the influence of the molar ratio between diether as internal donor and Magnesium dichloride in processing of the catalyst preparation on the catalytic performance for propylene polymerization with MgCl2‐supported Ziegler–Natta catalyst. The effect of electron donor on catalyst is investigated. The experimental data find that diether content on catalyst increases and Ti content on catalyst decreases with the increase of diether/Mg molar ratio. This result indicates that diether as internal donor is not coordinated to Ti species but to Mg species on catalyst. The introduction of diether remarkably improves the catalytic activity. The extents of improvement closely connect with diether/Mg molar ratio. The stereospecificity of catalyst intensively depends on the structure of diether as internal donor. The possible model of multi‐active sites on heterogeneous Ziegler–Natta catalyst is proposed to explain these phenomena. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1399–1404, 2006

Novel stabilization system for polypropylene via the Ziegler–Natta catalyzed polymerization in the presence of aluminum aryloxide

AbstractThe aluminum aryloxide was prepared via the reaction of phenolic antioxidant, 3‐(3,5‐di‐t‐butyl‐4‐hydroxyphenyl)‐N‐octadecylpropionamide, with triethyl aluminum. Propylene polymerization using supported Ziegler–Natta catalyst systems was carried out in the presence of the antioxidant or its aluminum aryloxide. Although the antioxidant gave rise to decrease in catalyst yield and change in hydrogen response, the aluminum aryloxide had no influence on the catalytic polymerization behavior, and thus the obtained polymer characteristics such as molecular weight, polydispersity, and meso pentad as a stereoregularity were comparable to that polymerized without the antioxidant and the aluminum aryloxide. Polypropylene obtained in the presence of the aluminum aryloxide was well stabilized for oxidation and its stability was over 1000 h at 100°C (estimated to be over 30 years at room temperature). © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 1350–1358, 2006

Synthesis and characterization of oligomer from 1-decene catalyzed by supported Ziegler–Natta catalyst

Oligomer of 1-decene was synthesized with Ziegler–Natta catalyst which consisted of TiCl 4 and Et 2AlCl, using MgCl 2 as support. The effects of temperature, Al/Ti ratio, time, and concentration of the catalyst on polymerization behaviors were investigated. The results showed that the catalyst system was desirable for the oligomerization of 1-decene with good catalytic activity, 143.8 kg oligo/mol Ti h, under typical conditions. The oligomer obtained was characterized with GC–MASS, GC and 13C NMR methods. Those results indicated that the oligomer was of a mixture consisting of di-, tri-, tetra- and pentamer. The 13C NMR data also implied that chain propagation of the oligomer involved primarily head-to-tail 1,2-insertions, as well as head-to-head and tail-to-tail 2,1-insertions.

Mechanism of olefin polymerization on supported Ziegler-Natta catalysts based on data on the number of active centers and propagation rate constants

The number of active centers (C g) and propagation rate constants (k g) for the polymerization of propylene and ethylene on highly active titanium-magnesium catalysts (TMCs) of different compositions at 70°C were determined using the method of 14CO inhibition of polymerization. In the polymerization of propylene on the TiCl4/D1/MgCl2-AlEt3/D2 system (D1 is dibutyl phthalate or 2,2′-diisobutyl-1,3-dimethoxypropane; D2 is a silane), the effects of D1 and D2 donors on the values of C g and k g were studied. It was found that the donors decreased the values of k g for nonstereospecific centers, had no effect on the values of k g for stereospecific centers, and increased the fraction of stereospecific centers, as well as the fraction of “sleeping” centers regardless of their stereospecificity. The rate constants of isotactic-chain transfer with C3H6, AlEt3, H2,and ZnEt2 were determined. In the polymerization of ethylene, a number of TMCs exhibited strong diffusion limitations, which manifested themselves in a dramatic decrease in the determined values of k g. It was demonstrated that diffusion limitations can be removed by decreasing the particle size and the concentration of active centers and by performing prepolymerization with propylene. The values of k g in ethylene polymerization were similar for stereospecific and nonstereospecific centers.

Study of propylene polymerization catalyzed by a spherical MgCl2‐supported Ziegler–Natta catalyst system: The effects of external donors

AbstractSpherical MgCl2‐supported Ziegler–Natta catalysts containing internal donors, such as diethyl phthalate, diisobutyl phthalate, and di‐n‐octyl phthalate, have been prepared. The effects of external donors, phenyltrimethoxysilane, phenyltriethoxysilane, and diphenyldimethoxylsilane, on the propylene polymerization catalyzed by these catalysts were studied. The results indicate that the external donors not only led to an increase in the isotactic index, but also affected the morphology of resultant polymer particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 738–742, 2005

Study on the distribution of active centers in novel low Ti-loading MgCl2-supported Ziegler-Natta catalyst

Study on the distribution of active centers in novel low Ti-loading MgCl₂-supported Ziegler-Natta catalyst