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     

Polymer-supported heterogeneous titanium-based Ziegler-Natta catalyst for ethylene polymerization

Reported here in, is the synthesis of polystyrene (PS)-supported Ziegler–Natta catalyst (PS-TiCl₄) by the reaction of PS and titanium tetrachloride (TiCl₄). PS was synthesized by emulsion polymerization using super critical CO₂ (sc-CO₂) as a medium. Three catalysts were synthesized by varying the TiCl₄/PS weight ratio in hexane medium. The resulting catalysts were characterized by Fourier transformed-infrared spectroscopy, UV–visible spectroscopy, scanning electron microscope and energy dispersive X-ray detector, X-ray diffraction analysis. The acidity of the catalysts in an acetone/water solution was measured by pH meter. The thermogravimetric analysis reveals that catalysts are stable upto 150–180°C. Due to their higher degree of thermal stability these catalysts may potentially be used as a support in conventional Ziegler–Natta catalyst for ethylene polymerization. These catalysts also showed good storability and its overall catalytic productivity are found to be 3720 g PE/g Ti. The productivity of the catalysts also depended on the titanium concentration in the polymer matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Different behaviors of metallocene and Ziegler–Natta catalysts in ethylene/1,5‐hexadiene copolymerization

The behaviors of three different catalyst systems, TiCl₄/MgCl₂, Cp₂ZrCl₂ and Cp₂HfCl₂, were investigated in ethylene/1,5‐hexadiene copolymerization. In the Fourier transform infrared spectra of the copolymers, cyclization and branching were detected for 1,5‐hexadiene insertion in the metallocene and Ziegler–Natta systems, respectively. DSC and viscometry analyses results revealed that copolymers with lower T_m and crystallinity and higher molecular weight were obtained with metallocene catalysts. The sequence length distribution of the copolymers was investigated by using the successive self‐nucleation and annealing thermal fractionation technique. The continuous melting endotherms obtained from successive self‐nucleation and annealing analysis were employed to get information about short‐chain branching, the branching dispersity index, comonomer content and lamella thickness in the synthesized copolymers. The results established that metallocene catalysts were much more effective than Ziegler–Natta catalysts in the incorporation of 1,5‐hexadiene in the polyethylene structure. Metallocene‐based copolymers had higher short‐chain branching and comonomer content, narrower branching dispersity index and thinner lamellae. Finally, the tendency of the employed catalysts in the 1,5‐hexadiene incorporation and cyclization reaction was explored via molecular simulation. The energy results demonstrated that, in comparison to Ziegler–Natta, metallocene catalysts have a much higher tendency to 1,5‐hexadiene incorporation and cyclization. © 2018 Society of Chemical Industry     

Control of molecular weight distribution in propylene polymerization with Ziegler–Natta/metallocene catalyst mixtures

Propylene polymerization was investigated with a sequential addition of Ziegler–Natta and metallocene catalysts. From the fact that the molecular weights of polypropylene (PP) produced with Ziegler–Natta and with metallocene catalysts differ, it was possible to control the molecular weight distribution (MWD) of PP with a sequential addition of methylaluminoxane and rac-ethylenebis(indenyl)zirconium dichloride followed by triethylaluminum and magnesium dichloride-supported titanium tetrachloride catalyst. The obtained PP exhibited a wide MWD curve with shoulder peak. The position and height of each peak was controlled with the variation of polymerization time for each catalyst as well as the amount of each catalyst. The MWD of PP prepared with sequential addition of catalysts was much wider than that of PP obtained from each catalyst. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 67:2213–2222, 1998     

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

A 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     

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     

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     

高分子载体负载Cp2ZrCl2/MAO催化剂及其催化乙烯聚合的研究

苯乙烯、2-乙烯基苯和烯丙基取代的茂金属催化剂进行共聚,合成高分子化的茂金属催化剂。该茂金属催化剂用于乙烯聚合反应活性较高,在聚合工艺条件为75 ℃,压力1.4 MPa,n(Al)∶n(Zr)=400时,活性可达1.95×10⁷ g·（mol·h）^－1,并可控制聚合物的形态。     

Butyl chloride as promoter in ethylene polymerization by magnesium ethoxide‐supported catalyst

The effects of butyl chloride as a promoter in the ethylene polymerization were studied using a Mg(OEt)₂/TiCl₄/triethyl aluminum (TEA) Ziegler–Natta catalyst system, where Mg(OEt)₂, TiCl₄, TEA were used as support, catalyst, and activator, respectively. The influence of BC on the catalyst performance, polymerization rate, and polymer properties were investigated. This study strongly indicates that BC could act as a promoter with high performance in the ethylene polymerization. There was a remarkable increase in the catalyst yield and polymerization rate, in particularly, in the presence of hydrogen which was used for controlling the molecular weight. A reduction in the polymer molecular weight was observed in the presence of BC and hydrogen. The morphology of the polymers was evaluated through scanning electron microscopy and particle size distribution. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40189.     

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     

Highly exfoliated PE/Na+MMT nanocomposite produced via in situ polymerization by a catalyst supported on a novel modified Na+MMT

A suitable Ziegler–Natta catalyst was prepared by supporting TiCl₄ on sodium montmorillonite (Na⁺MMT) modified by butyl octyl magnesium (BOM). This catalyst was applied for the polymerization of ethylene toward a polyethylene (PE)/Na⁺MMT nanocomposite. Catalyst behavior and nanocomposite properties were studied. It was found that catalyst activity was acceptably high. In addition, it had a smooth rate during ethylene polymerization. Transmission electron microscopy image and X-ray diffraction pattern evidenced an excellent exfoliation of the Na⁺MMT layers in the polymer matrix.     

Cp2TiCl2/坡缕石黏土负载型催化剂催化乙烯聚合的特性

利用浸渍法制备了两种二氯二茂钛（Cp₂TiCl₂）/坡缕石黏土负载型催化剂Cat-A 和Cat-B,并进行了乙烯淤浆聚合评价。对热活化黏土进行表征的结果表明,坡缕石黏土在热活化过程中由于配位结晶水的脱除表面主要由Lewis酸性位占据。黏土载体所具有的表面酸性使其具有完全不同于硅胶载体的负载茂金属催化剂聚合行为。在相同的聚合条件下,直接负载型催化剂的活性高于载体化学修饰型催化剂,甚至高于均相Cp₂TiCl₂催化剂。直接负载催化剂所得聚合产物的分子量和熔点低于载体化学修饰催化剂,且其产物性质受温度影响更为显著。以硅胶负载型茂金属催化剂作为对比,分析了表面具有较强Lewis酸性的载体活性中心性质,以此解释了直接负载型催化剂的乙烯聚合特性。对直接负载型催化剂不同时间段的聚合产物形态进行了扫描电镜观察,发现最终聚合产物中聚合物“纤维”和“纤维”聚集体形态的形成,并进一步分析了聚合物形态演化过程的特点。     

Reactor design and operation for gas-phase ethylene polymerization using ziegler-natta catalysts

A well-instrumented, semi-batch reactor has been constructed for studying the gas-phase polymerization of ethylene using solid Ziegler—Natta type catalysts. This reactor can be operated over the entire range of temperatures and pressures used in the commercial production of linear low, and high density polyethylenes. Successful operation of the reactor depends on careful control of the reaction temperature which in turn is mainly dependent on the total rate of polymerization. If this rate is too large, then the reaction temperature increases uncontrollably (thermal runaway) until catalyst deactivation occurs when melting polymer encapsulates the catalyst particles. Operating conditions are described which resulted in precise and reproducible kinetic measurements for a δ-TiCl₃ δ 1/3AlCl₃ catalyst (Stauffer AA Type 2.1) with diethylaluminum chloride (DEAC) as the co-catalyst. This system displayed first-order kinetic behavior over the temperature range 20 to 90°C with an activation energy of 32.6 kJ/mol.     

New clay‐supported Ziegler–Natta catalyst for preparation of PE/Clay nanocomposites via in situ polymerization

Polyethylene/clay (PE/Clay) nanocomposites were prepared by the in situ polymerization of ethylene using the new Clay/butyl octyl magnesium (BOM)/Chloroform/EtOH/TiCl₄/tri ethyl aluminum (TEA) catalyst system in heptane where BOM and TEA were the support for the clay modification and cocatalyst, respectively. The influence of the modified clay using BOM on the catalyst and polymerization was investigated. Also, the effect of temperature, pressure, hydrogen, and the molar ratios of TEA/Ti on the catalyst yield and ethylene consumption (polymerization rate) were studied. It was found that the above clay‐supported catalyst was an efficient Ziegler–Natta type catalyst due to its suitable yield for the polymerization of ethylene toward the production of the PE/Clay nanocomposites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Catalytic activity and control of the nascent morphology of polyethylenes obtained with first and second generation of Ziegler–Natta catalysts

The morphologies of the as-produced polyethylenes obtained by slurry polymerization process of ethylene in n-heptane, using heterogeneous conventional and supported Ziegler–Natta catalysts, were investigated. The ability of four different catalytic systems in controlling the size and shape of the nascent polymer particles were tested. The catalytic systems employed were: the original Ziegler type catalyst produced by reduction of TiCl₄ with Et₂AlCl, the Natta type catalyst TiCl₃–AA, the reduced TiCl₄ with the metal carbonyls [Mo(CO)₆ and Mn₂(CO)₁₀], and the supported TiCl₄ on three commercial silicas having different surface areas: Davison 951, 952, and also the Dart 1000. It was found that the carriers affect the catalytic activity of the final catalyst and also its kinetic behavior. The supported Ziegler–Natta catalysts control more easily the nascent polymer particles (size, shape, and porosity) than the conventional ones. In addition the morphology of the catalysts and the subsequent polymer particles are closely related to the parent morphology of the silicas used as carriers. Furthermore, the nascent morphology of the polyethylenes obtained with the conventional TiCl₄–Et₂AlCl catalytic system can be modified by using different |Al|/|Ti| ratios, resulting in more dense, spherical, and bigger polymer particles by increasing this ratio. On the other hand, detailed studies on the texture or arrangement of the polymer particles reveal the existence of mainly two fine morphologies (globular and wormlike), which are the result of the order of the primary or elementary catalyst particles (microspheres and platelets), the force linking them together, and the activity of the polymerization centers placed on their surface.     

烯烃聚合催化剂的研究进展

综述了Ziegler-Natta催化剂,茂金属催化剂和后过渡金属催化剂等烯烃聚合催化剂的最新研究进展,特别是前两者负载化的研究,并对Ziegler-Natta 经剂中给电子体作用机理,茂金属催化剂和后过渡金属催化剂应用于开发新型聚烯烃产品的探索做了详尽的叙述。     

Porous versus novel compact Ziegler–Natta catalyst particles and their fragmentation during the early stages of bulk propylene polymerization

The effect of the porosity of Ziegler–Natta catalyst particles on early fragmentation, nascent polymer morphology, and activity were studied. The bulk polymerization of propylene was carried out with three different heterogeneous Ziegler–Natta catalysts under industrial conditions at low temperatures, that is, with a novel self‐supported catalyst (A), a SiO₂‐supported catalyst (B), and a MgCl₂‐supported catalyst (C), with triethyl aluminum as a cocatalyst and dicyclopentyl dimethoxy silane as an external donor. The compact catalyst A exhibited no measurable porosity and a very low surface area (<5 m²/g) by Brunauer–Emmet–Teller analysis, whereas catalysts B and C showed surface areas of 63 and 250 m²/g, respectively. The surface and cross‐sectional morphologies of the resulting polymer particles at different stages of particle growth were analyzed by scanning electron microscopy and transmission electron microscopy. The compact catalyst A showed homogeneous and instantaneous fragmentation already in the very early stages of polymerization, which is typically observed for porous MgCl₂‐supported Ziegler–Natta catalysts. Moreover, the compact catalyst particles gave rise to almost perfectly spherical polymer particles with a smooth surface. In contrast, the silica‐supported catalyst B gave rise to particles having a cauliflower morphology, and the second reference catalyst C produced fairly spherical polymer particles with a rough surface. All of the three catalysts exhibited similar activities of 450 g of polypropylene/g of catalyst after 30 min of polymerization, and most interestingly, the comparative kinetic data presented indicated that the reaction rates were not influenced by the porosity of the catalyst. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.     

Behavior of poly(ethylene‐co‐olefin) polymers as elastomeric materials

The properties of two new ethylene‐α‐olefin copolymers, namely, ethylene–1‐hexene copolymer (EHC) and ethylene–1‐octadecene copolymers (EOC), synthesized via metallocene catalysts were evaluated. The copolymerization was carried out in an autoclave reactor with Et(Indenyl)₂ZrCl₂/methylaluminoxane as a catalyst system. These single‐site catalysts (metallocene type) allow one to obtain very homogeneous copolymers with excellent control of the molecular weight distribution and proportion of comonomer incorporation. So, copolymers with 18 mol % comonomer in the case of EHC and 12 mol % for EOC were shaped, and activities around 100,000 kg of polymer mol^?1 of Zr bar^?1 h^?1 were reached. The properties of these copolymers were compared with other commercial elastomers, such as ethylene–propylene copolymers synthesized by Ziegler–Natta catalysts and an ethylene–octene copolymer obtained via metallocene catalysts. The results show that these new copolymers, in particular, EOC, had excellent elastomeric properties. Furthermore, they had a relatively low viscosity, which implied a good response during processing. Moreover, the effectiveness of these copolymers as impact modifiers for polyolefins was also studied. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3008–3015, 2004     

Kinetics of ethylene polymerization at high temperature with Ziegler–Natta catalysts

A kinetic technique is developed for the study of ethylene polymerization reaction at high temperature with Ziegler–Natta catalysts. The technique is based on the calculation of polymerization rate parameters from the data on ethylene consumption vs. time. It takes into account increase of reaction temperature at the beginning of the reaction. Kinetic data in coordinates “polymerization rate–time” are presented for several pseudohomogeneous catalysts (TiCl₄? AlEt₂Cl, Ti(OiC₃H₇)₄? AlEt₂Cl), heterogeneous catalysts (δ-TiCl₃? AlEt₃, δ-TiCl₃? AlEt₂Cl, TiCl₄/MgCl₂? AlEt₃, TiCl₄/MgCl₂? AlEt₂Cl) and solubilized catalysts (δ-TiCl₃? poly-1-hexene? AlEt₂Cl) at 180°C and reaction pressure 14.6 atm for first 10 min of the reaction. These data are useful for the selection of Ziegler–Natta catalysts for testing in ethylene polymerization reaction in continuous high pressure reactors at short residence times.     

Effects of the catalyst system on the crystallization of polypropylene*

In search of a better understanding of catalyst effects on final product qualities of polypropylene, an attempt was made to establish a correlation between catalyst type, polymer chain structure of homopolymers, crystallization behavior, as well as final morphology and mechanical properties. Conventional Ziegler–Natta catalyst systems as well as novel metallocene catalysts were investigated, and influences of molar mass distribution and chain regularity were investigated as separate factors. Metallocene-based isotactic polypropylene shows some special effects regarding the nucleation density and the correlation between stereoregularity and mechanics that do not fit into the general picture for Ziegler–Natta catalyst based products. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2507–2515, 1999