Metallocene‐catalyzed olefin polymerization using magnesium chloride‐supported borate activators

New approaches have been identified for the immobilization, on a MgCl₂‐based support, of borate activators for metallocene‐catalyzed olefin polymerization. Immobilization of [HNEt₃][B(C₆F₅)₃(C₆H₄‐4‐OH)] was carried out by reaction with a support of type MgCl₂/AlR_n(OEt)_3?n, obtained by reaction of AlEt₃ with an adduct of magnesium chloride and ethanol. Use of the resulting immobilized borate in combination with zirconocene catalysts in ethylene and propylene polymerization resulted in significantly higher polymerization activities than were obtained using the same borate immobilized on a silica support. The MgCl₂‐based support also gave the better polymer particle morphology, cross‐sectional imaging indicating uniform support fragmentation, as opposed to incomplete fragmentation using the silica support. High catalyst activities were obtained using a MgCl₂/AlR_n(OEt)_3?n support impregnated with [Ph₃C][B(C₆F₅)₄]. In this case, a highly porous polyethylene particle morphology was obtained. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 986–993, 2006     

Hybrid titanium catalyst supported on core‐shell silica/poly(styrene‐co‐acrylic acid) carrier

Hybrid titanium catalysts supported on silica/poly(styrene‐co‐acrylic acid) (SiO₂/PSA) core‐shell carrier were prepared and studied. The resulting catalysts were characterized by Fourier transform infrared (FTIR) spectroscopy, laser scattering particle analyzer and scanning electronic microscope (SEM). The hybrid catalyst (TiCl₃/MgCl₂/THF/SiO₂·TiCl₄/MgCl₂/PSA) showed core‐shell structure and the thickness of the PSA layer in the two different hybrid catalysts was 2.0 μm and 5.0 μm, respectively. The activities of the hybrid catalysts were comparable to the conventional titanium‐based Ziegler‐Natta catalyst (TiCl₃/MgCl₂/THF/SiO₂). The hybrid catalysts showed lower initial polymerization rate and longer polymerization life time compared with TiCl₃/MgCl₂/THF/SiO₂. The activities of the hybrid catalysts were enhanced firstly and then decreased with increasing P/P. Higher molecular weight and broader molecular weight distribution (MWD) of polyethylene produced by the core‐shell hybrid catalysts were obtained. Particularly, the hybrid catalyst with a PSA layer of 5.0 μm obtained the longest polymerization life time with the highest activity (2071 kg PE mol^?1 Ti h^?1) and the resulting polyethylene had the broadest MWD (polydispersity index = 11.5) under our experimental conditions. The morphology of the polyethylene particles produced by the hybrid catalysts was spherical, but with irregular subparticles due to the influence of PSA layer. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Polymerization of ethylene and ethylene/1‐hexene over Ziegler‐Natta/Metallocene hybrid catalysts supported on SiO2 prepared by a sol‐gel method

A silica support for use in olefin polymerization was prepared by the gelation of a stable, colloidal phase of silica sol using a MgCl₂ solution as the initiator. The Ziegler‐Natta/Metallocene hybrid catalysts prepared using this support exhibited characteristics of both Ziegler‐Natta and metallocene catalysts. The polymers produced by the hybrid catalysts showed a bimodal molecular weight distribution pattern and two different melting points, corresponding to products arising from each catalyst. This suggests that the hybrid catalysts acted as individual active species and produced a blend of polymers. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2318–2326, 2000     

Synthesis mechanisms of poly[styrene‐co‐(acrylic acid)]‐supported TiCl4 catalysts modified by magnesium compounds

Soluble poly[styrene‐co‐(acrylic acid)] (PSA) modified by magnesium compounds was used to support TiCl₄. For ethylene polymerization, four catalysts were synthesized, namely PSA/TiCl₄, PSA/MgCl₂/TiCl₄, PSA/(n‐Bu)MgCl/TiCl₄, and PSA/(n‐Bu)₂Mg/TiCl₄. The catalysts were characterized by a set of complementary techniques including X‐ray photoelectron spectroscopy, Fourier‐transform infrared spectroscopy, X‐ray diffraction, thermogravimetric analysis, scanning electron microscopy, and element analysis. Synthesis mechanisms of polymer‐supported TiCl₄ catalysts were proposed according to their chemical environments and physical structures. The binding energy of Ti 2p in PSA/TiCl₄ was extremely low as TiCl₄ attracted excessive electrons from ? COOH groups. Furthermore, the chain structure of PSA was destroyed because of intensive reactions taking place in PSA/TiCl₄. With addition of (n‐Bu)MgCl or (n‐Bu)₂Mg, ? COOH became ? COOMg‐ which then reacted with TiCl₄ in synthesis of PSA/(n‐Bu)MgCl/TiCl₄ and PSA/(n‐Bu)₂Mg/TiCl₄. Although MgCl₂ coordinated with ? COOH first, TiCl₄ would substitute MgCl₂ to coordinate with ? COOH in PSA/MgCl₂/TiCl₄. Due to the different synthesis mechanisms, the four polymer‐supported catalysts correspondingly showed various particle morphologies. Furthermore, the polymer‐supported catalyst activity was enhanced by magnesium compounds in the following order: MgCl₂ > (n‐Bu)MgCl > (n‐Bu)₂Mg > no modifier. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Chemical composition distribution study in ethylene/1‐hexene copolymerization to produce LLDPE material using MgCl2‐TiCl4‐based Ziegler‐Natta catalysts

The characteristic features of LLDPE polymerization with ZN catalyst are the time drift effect during polymerization and the bending effect when trying to decrease density of the copolymer by adding more comonomer to the polymerization. The time drift in LLDPE polymerization is revealed by a constant decrease of comonomer incorporation during polymerization time. The bending is revealed by difficulties in lowering the density of LLDPE material below the density of 920 kg/m³. With increasing comonomer content during polymerization, the density does not decrease, but the soluble fraction increases. To try to observe if these phenomena are connected, two types of catalysts, SiO₂ supported and precipitated MgCl₂ ZN catalysts, were studied. A short time (10 min) and an extended time (60 min) copolymerization test series where the polymerizations were performed in the presence of a gradually increasing comonomer amount. Both catalysts show a strong bending when density is presented as a function of 1‐hexene both in 10‐ and 60‐min polymerization, indicating no connection between time drift and bending. The density, melting point, and crystallinity results all indicate that both catalysts are making similar copolymer material with identical chemical composition distribution. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of SiO2 porosity on activity profiles and comonomer incorporation in slurry ethylene/butene‐1 polymerization by (SiO2/MgCl2/TEOS/TiCl4) catalyst system

To investigate the influence of support porosity parameters e.g., average pore volume (APV), pore diameter (PD), and pore surface area distribution (PSAD) on activity‐profile of catalyst and comonomer incorporation, a series of silica‐supports with different porosity were prepared through sol–gel method and used to synthesize corresponding (SiO₂/MgCl₂/TEOS/TiCl₄) catalysts. Polymerization of ethylene/butene‐1 showed that increasing of APV from 0.75 to 2.2 cm³ g increase initial activity from 120 to 400 (g_poly/g_cat.bar.hr) followed by appearance of secondary peaks in activity‐profile which could be attributed to the variation of PSAD. It is found that the effect of support in polymerization is a complicated issue which depends not only on the porosity parameters also on the comonomer concentration. The catalyst with PD of 300 Å gives higher comonomer incorporation and polymers with 15–20% lower crystallinity in contrast to catalyst with PD of 100 Å. Porosity effect was quantitatively studied by modifying of conventional Z‐N catalyst polymerization mechanism through introducing fragmentation term to achieve a new tool in designing and developing of polyolefin catalysts. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Polymerization of ethylene using a SiO2–MgCl2 supported bis(cyclopentadienyl)zirconium(IV) or titanium(IV) dichloride catalyst

Silica supported MgCl₂–Cp₂MCl₂ (M = Ti or Zr) catalysts (Si–Mg–M) were prepared by deposition of a homogeneous solution of a metallocene and anhydrous magnesium chloride in tetrahydrofuran (THF) onto a high surface area silica (SiO₂). Catalyst thus prepared show higher polymerization activity when compared to metallocenes supported on either silica or magnesium chloride alone. The molecular weight and polydispersity of the poly(ethylene)s obtained from metallocenes supported on SiO₂–MgCl₂ were found to be higher and narrower, respectively, relative to silica or MgCl₂ supported metallocene catalysts. © 2002 Society of Chemical Industry     

The investigation of novel non‐metallocene catalysts with phenoxy‐imine ligands for ethylene (co‐)polymerization

Phthaldialdehyde and phthaldiketone were treated with substituted phenols of 2‐amino‐4‐methylphenol, 2‐amino‐5‐methylphenol and 2‐amino‐4‐t‐butylphenol, respectively, and then treated with transition metal halides of TiCl₄, ZrCl₄ and YCl₃. A series of novel non‐metallocene catalysts (1–12) with phenoxy‐imine ligands was obtained. The structures and properties of the catalysts were characterized by ¹H NMR and elemental analysis. The catalysts (1–12) were used to promote ethylene (co‐)polymerization after activation by methylaluminoxane. The effects of the structures and center atoms (Ti, Zr and Y) of these catalysts, polymerization temperature, Al/M (M = Ti, Zr and Y) molar ratio, concentration of the catalysts and solvents on the polymerization performance were investigated. The results showed that the catalysts were favorable for ethylene homopolymerization and copolymerization of ethylene with 1‐hexene. Catalyst 10 is most favorable for catalyzing ethylene homopolymerization and copolymerization of ethylene with 1‐hexene, with catalytic activity up to 2.93 × 10⁶ gPE (mol Y)^?1 h^?1 for polyethylene (PE) and 2.96 × 10⁶ gPE (mol Y)^?1 h^?1 for copolymerization of ethylene with 1‐hexene under the following conditions: polymerization temperature 50 °C, Al/Y molar ratio 300, concentration of catalyst 1.0 × 10^?4 L^?1 and toluene as solvent. The structures and properties of the polymers obtained were characterized by Fourier transform infrared spectroscopy, ¹³C NMR, wide‐angle X‐ray diffraction, gel permeation chromatography and DSC. The results indicated that the obtained PE catalyzed by 4 had the highest melting point of 134.8 °C and the highest weight‐average molecular weight of 7.48 × 10⁵ g mol^?1. The copolymer catalyzed by 4 had the highest incorporation of 1‐hexene, up to 5.26 mol%, into the copolymer chain. © 2012 Society of Chemical Industry     

Morphological study of spherical MgCl2.nEtOH supported TiCl4 Ziegler‐Natta catalyst for polymerization of ethylene

Spherical MgCl₂·nEtOH was prepared by adducting ethanol to MgCl₂ using melt quenching method. Effect of molar ratio of [EtOH]/[MgCl₂] = 2.8–3.05 on the morphology and particle size of the MgCl₂·nEtOH were studied. The best adduct of spherical morphology was obtained when 2.9 mol ethanol to 1 mol MgCl₂ was used. An emulsion of dissolved MgCl₂ in ethanol was prepared in a reactor containing silicon oil. Stirrer speed of the emulsion and its transfer rate to quenching section that work at ?10 to ?40°C are affected by the particle size of the adduct particle. The adducted ethanol was partially removed with controlled heat primary to catalyst preparation (support). Treatment of the support with excess TiCl₄ increased its surface area from 13.1 to 184.4 m²/g. Heterogeneous Ziegler‐Natta catalyst system of MgCl₂ (spherical)/TiCl₄ was prepared using the spherical support. Scanning electron microscopy studies of adduct, support, and catalyst obtained shown spherical particles, however, the polyethylene particles obtained have no regular morphology. The behavior indicates harsh conditions used for catalyst preparation, prepolymerization, and polymerization method used. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3829–3834, 2006     

Effect of ZnCl2‐ and SiCl4‐doped TiCl4/MgCl2/THF catalysts for ethylene polymerization

In this research, ethylene polymerization was carried out in the presence of different additives (ZnCl₂, SiCl₄, and the combined ZnCl₂‐SiCl₄) on TiCl₄/MgCl₂/THF catalytic system. The presence of ZnCl₂‐SiCl₄ mixtures showed higher activity in ethylene polymerization when compared with the catalytic activity in the presence of single Lewis acids, ZnCl₂, or SiCl₄. The modified catalyst with ZnCl₂‐SiCl₄ demonstrated the highest activity, which was more than three times the activity of the system without Lewis acid modification. The enhanced activity can be attributed to the reduction in the peak intensity of MgCl₂/THF complexes with Lewis acid compounds as proven by XRD. This was reasonable because of some THF removal from the structure of MgCl₂/THF by Lewis acid compounds. In addition to the effect of modification with additives on the partial elimination of THF, the catalytic activities could be increased due to the titanium atoms that have been locally concentrated on the surface as seen by energy dispersive X‐ray spectroscopy measurement. On the basis of the in situ electron spin resonance measurement, the mixed metal chlorides (ZnCl₂‐SiCl₄) addition could promote the amount of Ti³⁺after reduction with triethylaluminum. It revealed that the modification of TiCl₄/MgCl₂/THF catalytic system with mixed metal chlorides (ZnCl₂‐SiCl₄) is very useful for ethylene polymerization. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1588–1594, 2013     

Magnesium alkyl reduced titanium (IV) chloride based polymerization catalysts: materials rich in magnesium chloride

Reduction of TiCl₄ with organomagnesiums either in the presence of preformed MgCl₂, or concurrently with the formation of MgCl₂ from chlorocarbons, yields materials which are active catalysts for the polymerization of propene and ethene. Transformation of these materials to a violet allotrope by heating with TiCl₄ gives materials much more active for propene polymerization, albeit stereoregulation is still not good. interestingly, these transformed materials show little advantage for ethene polymerization except at high temperatures. Use of a Lewis base does not give high stereoregulation with propene; although some advantage is gained activity is greatly diminished by this.     

1,2‐Polymerization of 1,3‐butadiene with Cr(acac)3‐alkylaluminum catalysts

The polymerization of butadiene (Bd) with chromium(III) acetylacetonato [Cr(acac)₃]‐trialkylaluminum (AlR₃) or methylaluminoxane (MAO) catalysts was investigated for the synthesis of 1,2‐poly(Bd). The polymerization of Bd was found to proceed with Cr(acac)₃‐AlR₃ (R‐Me, Et, i‐Bu) catalysts to give poly(Bd) with a high 1,2‐vinyl content, but highly isotactic 1,2‐poly(Bd) was not synthesized. The Cr(acac)₃‐MAO catalyst gave a polymer consisting of low 1,2 units. The effects of the Al/Cr mole ratios on the polymerization of Bd with the Cr(acac)₃‐AlR₃ catalysts were observed. With an increase of Al/Cr mole ratios, the isotactic (mm) content of the polymer increased but the 1,2‐vinyl contents decreased. The effects of the aging time and temperatures of the catalysts on the polymerization of Bd with the Cr(acac)₃‐AlR₃ catalysts were also observed, and the lower polymerization temperature and the prolonged aging time were favored to produce the 1,2‐vinyl structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 1621–1627, 2000     

Studies on highly active coordination catalysts for polymerization of α-olefins: 3. Polymerization of propylene with MgCl2/TiCl4/AlEt3 or MgCl2/PhCOOC2H5/TiCl4/AlEt3 systems

Activity and stereospecificity of the $\text{MgCl}{}_2\text{TiCl}{}_4$ catalyst in the polymerization of propylene follow curves showing maxima with grinding time of the MgCl₂ support. Using MgCl₂/PhCOOC₂H₅/TiCl₄ catalysts, no decrease in activity and stereospecificity was observed presumably because of complex formation between MgCl₂ support and ethyl benzoate.     

Preparation of novel microspherical MgCl2‐based titanium catalyst for propylene polymerization

Lowering the particle size of support is one of methods to reduce breakage of supported catalyst during polymerization, which may cause serious problems for fine polymer particles from those broken catalysts. Microspheric MgCl₂ support could be obtained by emulsion way, but we found that they easily aggregated after emulsification and they are difficult to keep good spherical morphology. Up until now, hardly paper on the morphology improvement of micro size supports has been published. With the addition of an amount of Poly(propylene glycol)(PPG), microspheric MgCl₂ supports with good morphology were obtained. 1, 3, 15, 35, 80% PPG were added, respectively, and the results of SEM study on obtained particles showed that appropriate addition of PPG obviously improved the morphology of supports. The optimist dosage was 3% in our experiment and the activity of catalyst supported on obtained support was 32.3 kg PP/g cat h. The function of PPG was explored preliminarily. In spite of the improvement of morphology the activity of supported catalyst was decreased gradually compared to those without PPG. So the further XRD and IR analysis were carried out to find reasons. The results indicated that PPG might plug pores of support and interfere with the reaction between supports and TiCl₄. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Modeling of the propylene polymerization catalyzed by single‐/multi‐active site catalyst: A Monte Carlo study

In the present study, a model is established to describe the propylene polymerization kinetics catalyzed by the typical catalysts with single‐/multi‐active site type in a liquid phase stirred‐tank reactor using the Monte Carlo simulation method, regardless of the mass and heat diffusion effects within the polymer particles. Many kinetic data, including polypropylene yield, concentration transformation of catalyst active sites, number–average molecular weight, etc., are obtained by the model. The simulated kinetic results are found to be in agreement with the reference ones obtained in a population balance model. Furthermore, the comparisons of the kinetic data between the polymerization catalyzed by the catalyst with single‐active site type (typically silica‐supported metallocene) and the catalyst with multi‐active site type (typically MgCl₂‐supported Ziegler‐Natta catalyst) have been studied using the model. Especially, the effects of hydrogen on the polymerization are studied using the model. The studied results show that the theory of catalyst active site can be used to explain the different propylene polymerization kinetics catalyzed by the typical catalyst with single‐/multi‐active site type. In addition, the role of hydrogen in the propylene polymerization needs to be emphasized. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Kinetic and morphological study of a magnesium ethoxide‐based Ziegler–Natta catalyst for propylene polymerization

BACKGROUND: Kinetic and morphological aspects of slurry propylene polymerization using a MgCl₂‐supported Ziegler–Natta catalyst synthesized from a Mg(OEt)₂ precursor are investigated in comparison with a ball‐milled Ziegler–Natta catalyst. RESULTS: The two types of catalyst show completely different polymerization profiles: mild activation and long‐standing activity with good replication of the catalyst particles for the Mg(OEt)₂‐based catalyst, and rapid activation and deactivation with severe fragmentation of the catalyst particles for the ball‐milled catalyst. The observed differences are discussed in relation to spatial distribution of TiCl₄ on the outermost part and inside of the catalyst particles. CONCLUSION: The Mg(OEt)₂‐based Ziegler–Natta catalyst is believed to show highly stable polymerization activity and good replication because of the uniform titanium distribution all over the catalyst particles. Copyright © 2008 Society of Chemical Industry     

Polymerization of ethylene and ethylene/1-hexene over Ziegler–Natta/metallocene hybrid catalysts supported on MgCl2 prepared by a recrystallization method

MgCl₂ for use as a catalyst support was prepared by dissolution in methanol and recrystallization in n-decane, followed by vacuum-drying at 2,000 rpm. The prepared support was modified by treatment with alkylaluminum compounds. The activity profile of ethylene over the supported catalysts persisted for periods up to 1 h during the polymerization. The prepared Ziegler–Natta/metallocene hybrid catalysts exhibited the characteristics of both metallocene and Ziegler–Natta catalysts. The polymer produced by the hybrid catalysts gave bimodal peaks in differential scanning calorimetry analysis for ethylene and ethylene/1-hexene polymerization, suggesting that the polymer was composed of two different lamellar structures that were polymerized by each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 1707–1715, 1998     

Molecular weight distribution of polyethylene catalyzed by Ziegler–Natta catalyst supported on MgCl2 doped with AlCl3

Ti‐based Ziegler–Natta catalysts supported on MgCl₂ doped with AlCl₃ were prepared by the reaction of MgCl₂/AlCl₃–ethanol adduct with TiCl₄. No AlCl₃ crystallites were found in the AlCl₃‐doped catalysts by WAXD analysis, suggesting that AlCl₃/MgCl₂ solid solution was formed. The effect of doping on the catalyst performance in ethylene polymerization was investigated. The results showed that the catalysts based on AlCl₃‐doped MgCl₂ support exhibited a slightly higher activity than did the MgCl₂‐supported catalyst and the molecular weight distribution (MWD) of polyethylene (PE) markedly increased (from 10.8 to 47.9) with the increase of AlCl₃ content in catalysts. The changes in catalyst's active center distribution were studied based on nonlinear fitting of the polymer GPC curves by multiple Flory functions. It was found that increase of types of active centers by introducing AlCl₃ into the support should be responsible for the broadening of MWD of PE. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 1768–1772, 2006     

Preparation of novel MgCl2‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization

In this article, preparation of novel MgCl₂‐adduct supported spherical Ziegler–Natta catalyst for α‐olefin polymerization is reported. The factors affecting the particle size (PS) and particle size distribution (PSD) of the prepared support were investigated. In this method, the internal donor added while preparing MgCl₂‐adduct support was supposed to act as a crosslinking agent. Therefore it provided a reasonable way to enhance the morphology and control the PS of the resultant polymer particles. The possible mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 945–948, 2006     

Organic/inorganic support for immobilizing (n‐BuCp)2ZrCl2/TiCl3 hybrid catalyst for use in the preparation of polymer blends

Reactor blends of ultrahigh‐molecular‐weight polyethylene (UHMWPE) and low‐molecular‐weight polyethylene (LMWPE) were synthesized by two‐step polymerization using a hybrid catalyst. To prepare the hybrid catalyst, styrene acrylic copolymer (PSA) was first coated onto SiO₂/MgCl₂‐supported TiCl₃; then, (n‐BuCp)₂ZrCl₂ was immobilized onto the exterior PSA. UHMWPE was produced in the first polymerization stage with the presence of 1‐hexene and modified methylaluminoxane (MMAO), and the LMWPE was prepared with the presence of hydrogen and triethylaluminium in the second polymerization stage. The activity of the hybrid catalyst was considerable (6.5 × 10⁶ g PE (mol Zr)^?1 h^?1), and was maintained for longer than 8 h during the two‐step polymerization. The barrier property of PSA to the co‐catalyst was verified using ethylene polymerization experiments. The appearance of a lag phase in the kinetic curve during the first‐stage polymerization implied that the exterior catalyst ((n‐BuCp)₂ZrCl₂) could be activated prior to the interior catalyst (M‐1). Furthermore, the melting temperature, crystallinity, degree of branching, molecular weight and molecular‐weight distribution of polyethylene obtained at various polymerization times showed that the M‐1 catalyst began to be activated by MMAO after 40 min of the reaction. The activation of M‐1 catalyst led to a decrease in the molecular weight of UHMWPE. Finally, the thermal behaviors of polyethylene blends were investigated using differential scanning calorimetry. Copyright © 2011 Society of Chemical Industry