Modification of a Ziegler-Natta catalyst with a metallocene catalyst and its olefin polymerization behavior

A Ziegler-Natta catalyst was modified with a metallocene catalyst and its polymerization behavior was examined. In the modification of the TiCl₄ catalyst supported on MgCl₂ (MgCl₂-Ti) with a rac-ethylenebis(indenyl)zirconium dichloride (rac-Et(Ind)₂ZrCl₂, EIZ) catalyst, the obtained catalyst showed relatively low activity but produced high isotactic polypropylene. These results suggest that the EIZ catalyst might block a non-isospecific site and modify a Ti-active site to form highly isospecific sites. To combine two catalysts in olefin polymerization by catalyst transitioning methods, the sequential addition of catalysts and a co-catalyst was tried. It was found that an alkylaluminum like triethylaluminum (TEA) can act as a deactivation agent for a metallocene catalyst. In ethylene polymerization, catalyst transitioning was accomplished with the sequential addition of bis(cyclopentadienyl)zirconium dichloride (Cp₂ZrCl₂)/methylaluminoxane (MAO), TEA, and a titanium tetrachloride/vanadium oxytrichloride (TiCl₄/VOCl₃, Ti-V) catalyst. Using this method, it was possible to control the molecular weight distribution (MWD) of polyethylene in a bimodal pattern. In the presence of hydrogen, polyethylene with a very broad MWD was obtained due to a different hydrogen effect on the Cp₂ZrCl₂ and Ti-V catalyst. The obtained polyethylene with a broader MWD exhibited more apparent shear thinning.     

Preparation of inorganic MgCl2-alcohol adduct and its application in organometallic HYBRID catalysts for ethylene polymerization

Inorganic support, MgCl₂-alcohol adduct, for use in the impregnation of organometallic catalysts, was prepared by the recrystallization method using alcohol. Since MgCl₂-alcohol adduct has two functional groups in the molecule, i.e., hydroxyl (-OH) and chlorine (-Cl) groups, it is suitable for the impregnation of both metallocene and Ziegler-Natta hybrid catalysts. The hybrid catalysts were prepared in order to control the molecular weight (Mw) and the molecular weight distribution (MWD) in ethylene polymerization. The polyethylene produced by the Ziegler-Natta/Metallocene hybrid catalysts showed two melting temperatures and a bimodal MWD, corresponding to products arising from each of the individual catalysts. This suggests that these hybrid catalysts acted as individual active species and produced a blend of polymers. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Effect of cocatalyst on the chemical composition distribution and microstructure of ethylene-hexene copolymer produced by a metallocene/Ziegler-Natta hybrid catalyst

A silica-magnesium bisupport (SMB) was prepared by a sol-gel method for use as a support for metallocene/Ziegler-Natta hybrid catalyst. The SMB was treated with methylaluminoxane (MAO) prior to the immobilization of TiCl₄ and rac-Et(Ind)₂ZrCl₂. The prepared rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst was applied to the ethylenehexene copolymerization with a variation of cocatalyst species (polymerization run 1: triisobutylaluminum (TIBAL) and methylaluminoxane (MAO), polymerization run 2: triethylaluminum (TEA) and methylaluminoxane (MAO)). The effect of cocatalysts on the chemical composition distributions (CCDs) and microstructures of ethylene-hexene copolymers was examined. It was found that the catalytic activity in polymerization run 1 was a little higher than that in polymerization run 2, because of the enhanced catalytic activity at the initial stage in polymerization run 1. The chemical composition distributions (CCDs) in the two copolymers showed six peaks and exhibited a similar trend. However, the lamellas in the ethylene-hexene copolymer produced in polymerization run 1 were distributed over smaller sizes than those in the copolymer produced in polymerization run 2. It was also revealed that the rac-Et(Ind)₂ZrCl₂/TiCl₄/MAO/SMB catalyst preferably produced the ethylene-hexene copolymer with non-blocky sequence when TEA and MAO were used as cocatalysts.     

Control of molecular weight distribution (MWD) for polyethylene catalyzed over Ziegler-Natta/Metallocene hybrid catalysts

Two types of inorganic supports, MgCl₂ and SiO₂, for the impregnation of catalysts were prepared by the recrystallization and sol-gel methods, respectively. The Ziegler-Natta/Metallocene hybrid catalysts were prepared in order to control the molecular weight (Mw) and the molecular weight distribution (MWD) during ethylene polymerization. The polyethylene produced by the hybrid catalysts can control the Mw and the MWD of polymer, showing two melting temperatures and a bimodal MWD, corresponding to products arising from each of the individual catalysts. This suggests that these hybrid catalysts acted as individual active species and produced a blend of polymers. This paper was presented at the 8th APCChE (Asia Pacific Confederation of Chemical Engineering) Congress held at Seoul between August 16 and 19, 1999.     

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     

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     

The influence of the preparing conditions of SiO2 supported Cp2ZrCl2 catalyst on ethylene polymerization

In this work, ethylene was polymerized by using Cp₂ZrCl₂ supported on silica pretreated with methylaluminoxane (MAO) as the catalyst system. The influence of the conditions for the preparation of the heterogeneous catalyst, such as temperature, washing method of the catalytic solid, MAO and metallocene concentration in the support treatment, time of MAO, and metallocene immobilization on the support, type of alkylaluminum used in the support pretreatment, and calcination temperature of the support were investigated. Aluminum and zirconium content fixed on the silica surface were determined by inductively coupled plasma emission spectroscopy. Polymer characteristics were determined by gel permeation chromatography and differential scanning calorimetry. According to the results, the activity of some supported catalysts were far higher than with the homogeneous system. Moreover, polyethylene with very high molecular weights were also obtained and with molecular weight distribution larger than those produced with the homogeneous precursor. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2054–2061, 2002     

Development of novel chromium oxide/metallocene hybrid catalysts for bimodal polyethylene

The investigation of a multicomponent catalyst in polyolefin field came up as an alternative for synthesizing bimodal polymers in only one step process under constant reaction conditions.In the present work, new bifunctional catalysts were prepared by combining chromium and metallocene species on the same solid and tested in ethylene polymerization in order to evaluate the possibility of producing bimodal polyethylene. The catalytic system methylaluminoxane (MAO)/(nBuCp)₂ZrCl₂ was immobilized on activated chromium catalysts supported onto several inorganic carriers (silica, silica-alumina, aluminophosphate and mesostructured SBA-15-type materials). The reaction results showed a clear influence of the physicochemical properties of the support on the relative contribution of metallocene and chromium centers as well as on polymers molecular weight distribution. A bimodal polyethylene was obtained by supporting the MAO/metallocene system on a mesostructured chromium catalyst prepared by direct synthesis.     

Ethylene slurry polymerization using nickel diimine catalysts covalently-attached onto MgCl2-based supports

MgCl₂/alcohol adducts were recrystallized with alkyl aluminums and used as catalysts supports for nickel diimine complexes functionalized with amine groups. These supported catalysts were used to polymerize ethylene in a slurry reactor. The MgCl₂-based supported nickel diimine catalysts had higher activities than the equivalent SiO₂-supported nickel diimine catalysts, even without the use of activators. These catalysts made polyethylene with melting temperatures and molecular weights higher than those made with the equivalent homogeneous catalysts. Interestingly, the catalyst activity and polymer molecular weight could be controlled by changing the support composition. In addition, covalent chemical bonds between the functionalized nickel diimine complex and the MgCl₂-based supports avoided catalyst leaching during polymerization, leading to the production of polymer particles with good morphology. The mechanical strength of the resulting polymer particles, however, was lower than those made with SiO₂-supported nickel diimine catalysts.     

无机/有机复合载体SiO_2/MgCl_2·xBu(OH)_2/PSA负载TiCl_4催化剂的制备及其乙烯聚合行为

采用SiO2、MgCl2以及苯乙烯-丙烯酸共聚物(PSA)合成了SiO2/MgCl2.xBu(OH)2/PSA无机/有机复合载体并负载TiCl4,得到具有SiO2无机支撑层、MgCl2.xBu(OH)2加合物以及PSA有机载体3种化学环境的SiO2/MgCl2.xBu(OH)2/PSA/TiCl4复合载体负载催化剂。研究了复合载体组成对催化剂的载钛量、形貌以及乙烯聚合行为的影响。当PSA存在时,催化剂的载钛量明显降低。乙烯/1-己烯共聚的反应动力学结果表明,与SiO2/MgCl2.xBu(OH)2/TiCl4相比,无机/有机复合载体负载催化剂的动力学曲线具有一段较长的受扩散控制的诱导期,并且随着PSA质量分数的增加,诱导期延长,动力学曲线由衰减型转变为上升-稳定型。由于复合载体具有多种化学环境,使得负载催化剂活性中心种类增多,共聚性能提高,聚乙烯产品分子量分布变宽,熔流比显著提高。根据聚乙烯树脂的扫描电镜照片,探讨了复合载体负载催化剂在聚乙烯生长过程中的破碎机理。     

Surface science studies of Ziegler-Natta olefin polymerization system: Correlations between polymerization kinetics, polymer structures, and active site structures on model catalysts

The surface composition and structure of model Ziegler-Natta catalysts, polymerizing α-olefins to produce polyolefins, have been studied using modern surface science techniques and compared with their polymerization behaviors. Two types of thin films — TiCl_x/MgCl₂ and TiCl_y/Au — were fabricated on an inert gold substrate, using chemical vapor deposition methods, to model the high-yield catalysts of MgCl₂-supported TiCl₄ and TiCl₃-based catalysts, respectively. The model catalysts could be activated by exposure to triethylaluminum (AlFt₃) vapor. Once activated, both catalysts were active for polymerization of ethylene and propylene in the absence of excess AlEt₃ during polymerization. The model catalysts had polymerization activities comparable to the high-surface-area industrial catalysts. Though both catalysts were terminated with chlorine at the surface, each catalyst assumed different surface structures. The TiCl_x/MgCl₂ film surface was composed of two structures: the (001) basal plane of these halide crystallites and a non-basal plane structure. The TiCl_y/Au film surface assumed only the non-basal plane structure. These structural differences resulted in different tacticity of the polypropylene produced with these catalysts. The TiCl_x/MgCl₂ catalyst produced both atactic and isotactic polypropylene, while the TiCl_y/Au catalyst without the MgCl₂ support produced exclusively isotactic polypropylene. The titanium oxidation state distribution did not have a critical role in determining the tacticity of the polypropylene.     

Plausible guard effect on the active sites of heterogeneous Ziegler–Natta catalyst by coordinating monomers and growing polymer chains in the initial stage of propene polymerization

Investigation of propene polymerization by a modified stopped‐flow technique using TiCl₄/ethylbenzoate(EB)/MgCl₂ Ziegler–Natta catalyst with or without pretreating the catalyst with triethylaluminium (TEA) within an ultra‐short period (ca 1 s) was conducted to gain new understanding of the nature of active sites related to TEA in the early stage of polymerization. When the catalyst was pretreated by a cocatalyst, deactivation behaviour was clearly observed, even within an extremely short pretreatment period. In contrast, without pretreatment, the deactivation of active sites can be neglected within the polymerization period indicating that the activated Ti species might be protected from deactivation by TEA when monomer is present in the system. A plausible guard effect on the active sites by coordinating monomer and growing polymer chains in the initial stage of polymerization is proposed to account for this phenomenon. Copyright © 2004 Society of Chemical Industry     

Influence of supported vanadium catalyst on ethylene polymerization reactions

BACKGROUND: In the research area of homogeneous Ziegler–Natta olefin polymerization, classic vanadium catalyst systems have shown a number of favourable performances. These catalysts are useful for (i) the preparation of high molecular weight polymers with narrow molecular weight distributions, (ii) the preparation of ethylene/R‐olefin copolymers with high R‐olefin incorporation and (iii) the preparation of syndiotactic polypropylenes. In view of the above merits of vanadium‐based catalysts for polymerization reactions, the development of well‐defined single‐site vanadium catalysts for polymerization reactions is presently an extremely important industrial goal. The main aim of this work was the synthesis and characterization of a heterogeneous low‐coordinate non‐metallocene (phenyl)imido vanadium catalyst, V(NAr)Cl₃, and its utility for ethylene polymerization. RESULTS: Imido vanadium complex V(NAr)Cl₃ was synthesized and immobilized onto a series of inorganic supports: SiO₂, methylaluminoxane (MAO)‐modified SiO₂ (4.5 and 23 wt% Al/SiO₂), SiO₂? Al₂O₃, MgCl₂, MCM‐41 and MgO. Metal contents on the supported catalysts determined by X‐ray fluorescence spectroscopy remained between 0.050 and 0.100 mmol V g^?1 support. Thermal stability of the catalysts was determined by differential scanning calorimetry (DSC). Characterization of polyethylene was done by gel permeation chromatography and DSC. All catalyst systems were found to be active in ethylene polymerization in the presence of MAO or triisobutylaluminium/MAO mixture (Al/V = 1000). Catalyst activity was found to depend on the support nature, being between 7.5 and 80.0 kg PE (mol V)^?1 h^?1. Finally, all catalyst systems were found to be reusable for up to three cycles. CONCLUSION: Best results were observed in the case of silica as support. Acid or basic supports afforded less active systems. In situ immobilization led to higher catalyst activity. The resulting polyethylenes in all experiments had ultrahigh molecular weight. Finally, this work explains the synthesis and characterization of reusable supported novel vanadium catalysts, which are useful in the synthesis of very high molecular weight ethylene polymers. Copyright © 2007 Society of Chemical Industry     

Synthesis of branched polyethylene by in situ polymerization of ethylene with combined iron catalyst and Ziegler–Natta catalyst

2,6‐Bis(imino)pyridyl iron catalyst and traditional Ziegler–Natta catalyst were combined together as tandem catalytic system, activated with the mixture of TEA and MAO, and used for synthesis of branched polyethylene by in situ polymerization of ethylene. The branched polyethylene with branches from 8/1000C to 29/1000C was produced by adjusting reaction conditions: the amount of TEA, MAO, iron catalyst used, and reaction temperatures. Not only the short branches such as ethyl and butyl but also the longer branches (hexyl and longer than hexyl) were detected in the products. The products exhibited higher molecular weight and broader molecular weight distribution than those obtained from metallocene catalysts, which would provide the materials excellent mechanical properties and processability. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

Characteristics of ethylene polymerization over Ziegler–Natta/metallocene catalysts Comparison between hybrid and mixed catalysts

Two types of inorganic supports, MgCl₂ and SiO₂, for the impregnation of catalysts were prepared by the recrystallization and the sol–gel method, respectively. The polyethylene produced by the Ziegler–Natta/metallocene hybrid and mixed catalysts showed two melting temperatures and a bimodal MWD corresponding to products arising from each of the individual catalysts. This suggests that these Ziegler–Natta/metallocene catalysts acted as individual active species, and as a result, produced a blend of polymers.     

Modification of Ziegler-Natta catalysts by cyclopentiadienyl-type ligands: Activation of titanium-based catalysts

Conventional Ziegler-Natta catalysts, based on TiCl₄ supported on MgCl₂, were modified by substituting a part of the chlorides by cyclopentadienyl (and derivatives) ligands. Although these catalysts are very active (activities up to 10⁵ g PE/g catalyst/h) they exhibit a conventional Ziegler-Natta behavior (methylaluminoxane is not necessary, polyethylene produced with a rather broad molar weight distribution, low sensitivity to hydrogen). It was attributed to cluster effects: an increase of the number of conventional TiCl₄ active sites by adding cyclopentadienyl ligands on titanium neighbors. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 2281–2288, 1997     

Silica‐supported (nBuCp)2ZrCl2: effect of catalyst active center distribution on ethylene–1‐hexene copolymerization

Metallocenes are a modern innovation in polyolefin catalysis research. Therefore, two supported metallocene catalysts—silica/MAO/(ⁿBuCp)₂ZrCl₂ (Catalyst 1) and silica/ⁿBuSnCl₃/MAO/(ⁿBuCp)₂ZrCl₂ (Catalyst 2), where MAO is methylaluminoxane—were synthesized, and subsequently used to prepare, without separate feeding of MAO, ethylene–1‐hexene Copolymer 1 and Copolymer 2, respectively. Fouling‐free copolymerization, catalyst kinetic stability and production of free‐flowing polymer particles (replicating the catalyst particle size distribution) confirmed the occurrence of heterogeneous catalysis. The catalyst active center distribution was modeled by deconvoluting the measured molecular weight distribution and copolymer composition distribution. Five different active center types were predicted for each catalyst, which was corroborated by successive self‐nucleation and annealing experiments, as well as by an extended X‐ray absorption fine structure spectroscopy report published in the literature. Hence, metallocenes impregnated particularly on an MAO‐pretreated support may be rightly envisioned to comprise an ensemble of isolated single sites that have varying coordination environments. This study shows how the active center distribution and the design of supported MAO anions affect copolymerization activity, polymerization mechanism and the resulting polymer microstructures. Catalyst 2 showed less copolymerization activity than Catalyst 1. Strong chain transfer and positive co‐monomer effect—both by 1‐hexene—were common. Each copolymer demonstrated vinyl, vinylidene and trans‐vinylene end groups, and compositional heterogeneity. All these findings were explained, as appropriate, considering the modeled active center distribution, MAO cage structure repeat units, proposed catalyst surface chemistry, segregation effects and the literature that concerns and supports this study. While doing so, new insights were obtained. Additionally, future research, along the direction of the present work, is recommended. © 2013 Society of Chemical Industry     

Effect of the cocatalyst on the copolymerization of propylene and small amount of ethylene with high activity Ziegler-Natta catalyst

Summary The copolymerization of propylene with small amount of ethylene using MgCl₂-supported stereospecific catalysts in combination with different Al-alkyls was performed. At least for the particular catalyst used, it resulted that TEA and TIBA are the preferred Al-alkyls; whereas, the mixture TEA/DEAC provides copolymers with a high amount of xylene solubles. Finally, the mixture TEA/DEAI largely decreases catalyst activity, but it provides a copolymer with broad MMD.     

负载型茂金属催化剂用于乙烯淤浆聚合的研究

在烯烃催化聚合领域,茂金属催化剂显示出比传统Ziegler-Natta催化剂更高的活性。以苯甲酸催化三甲基铝（TMA）受控水解生成甲基铝氧烷（MAO）,经热解过程后合成了一种不溶形式的固体聚甲基铝氧烷（sMAO）。以合成的sMAO为载体负载茂金属催化剂,并将该催化剂应用于乙烯淤浆聚合反应中,系统探究了聚合条件对催化行为的影响,同时对聚乙烯产品mPE的粒度、堆密度、分子量及分布和熔体流动速率等基本理化性能进行了分析表征。实验结果表明,制备的催化剂颗粒形态较好,粒子分布均匀,在5 L釜中催化淤浆反应,乙烯/1-己烯共聚活性最高可达15 302.6 g·g^-1,并得到了相对分子质量分布均匀的中、高密度聚乙烯产品。     

分子量宽峰分布聚乙烯茂金属催化剂的研究

以复合茂金属催化剂和双载体茂金属催化剂乙烯聚合、考察聚乙烯（ＰＥ）分子量分布变化情况。结果发现两者都使ＰＥ分子量分布加宽,其中复合茂金属催化剂Ｃｐ２ＺｒＣｌ２／ＹＢ３使分子量分布从２．３７增至９．１８。分子量分布增加幅度与不同复合茂经剂、催化剂配比、２载体量之比负载催化剂用量有关。