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     

Preparation and properties of isotactic polypropylene obtained from MgCl2-supported TiCl4 catalyst bearing bifunctional internal donor

In this research, a novel MgCl₂-supported TiCl₄ catalyst in conjunction with bifunctional internal donor was synthesized. The effects of internal donor on propylene polymerization behaviors and polymer properties (morphology, M _w and MWD) were investigated. It was found that the activity of novel catalyst was higher than that of the traditional DIBP-based Ziegler–Natta catalyst, while the catalyst activity was less influenced by the ether group length of the bifunctional internal donor. It was also observed that the MWD of PP obtained by bifunctional internal donor-based catalyst was broader than that of PP made by DIBP-based Ziegler–Natta catalyst.     

Retrofitting of industrial olefin polymerization plants: producing broad MWDs through multiobjective periodic operation

The drop‐in of metallocene catalysts (MCs) in existing industrial polymerization plants is the current goal of most polymer producers. However, the narrow molecular weight distribution (MWD) of the polymers produced by MCs prevent them of moving into commodities market dominated by conventional Ziegler–Natta catalysts, where ease of processing is an essential property. Broader MWDs may be obtained through mixing of different MCs or blending of different resins, but resin‐compatibility problems and complex undesirable catalyst interactions pose technological problems that have yet to be solved. For these reasons, modern olefin polymerization plants have to work with both catalysts to respond to market demands, resulting in costly operations of grade/catalyst change. In this article, we describe how periodic control of short residence‐time reactors operating with an MC (Me₂Si(2‐Me‐Benz[e]Ind)₂ZrCl₂/MAO) can lead to polymers with broad MWD and, consequently, to high processability. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 437–452, 2000     

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     

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     

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     

The influence of combined external donor and combined cocatalyst on propylene polymerization with a MgCl2‐supported Ziegler–Natta catalyst in the presence of hydrogen

The influence of combined external donor (ED) (diphenyldimethoxysilane/dicyclopentyldimethoxysilane) and combined cocatalyst (triethylaluminum/triisobutylaluminum) on propylene polymerization with MgCl₂‐supported Ziegler–Natta catalyst in the presence of hydrogen was investigated. By deconvolution analysis of the molecular weight distribution (MWD) into multiple Flory components, the influence of ED and cocatalyst on the active center distribution of the catalyst was demonstrated, and the mechanism was discussed. Using combined cocatalyst and combined donor, iPP with high molecular weight, high isotacticity index, and broad MWD can be obtained. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41689.     

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。     

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。     

The production of high efficiency Ziegler–Natta catalyst with dual active sites nature using cyclohexyl chloride as promoter with super activity and produced superior polyethylene with controllable molecular weight distribution

In the previous studies, the several halocarbons (HC) were tested as promoters for a Ti-based Ziegler–Natta (ZN) catalyst at different polymerization conditions. The Results showed that chloro cyclohexane has the best operation in catalyst activity, polymer particle size growth, hydrogen responsibility and wax reduction too. For the first time in this study, the effect of Al/Ti ratio on the optimum HC/Ti ratio has been considered and the results showed that the optimum HC/Ti ratio depends on the Al/Ti ratio directly. In the optimum HC/Ti ratio, the catalyst activity and hydrogen responsibility ratio of the catalyst increase up to 125 and 55% respectively. The acceptable growth of polymer powder up to 46%, lower flow rate ratio (FRR) up to 19% and decrease of wax amount up to 12%, completed the promotion results. Furthermore, in the next part of this study and as key note, a little dose of halocarbon was used in the catalyst preparation to produce the special catalysts with dual active sites. In the catalyst preparation, the concentration of each active sites depends on the halocarbon amount and it can control the molecular weight distribution of the produced polyethylene; because each active sites have different response to hydrogen. The halocarbon based catalysts showed the remarkable effect on the catalyst activity, the molecular weight and especially molecular weight distribution (MWD). The flow rate ratio and MWD could be increased up to 77 and 88% respectively as the main result of halocarbon addition during the catalyst preparation.     

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.     

Comparative effect of metallocene and Ziegler‐Natta polypropylene on the exfoliation of montmorillonite and hectorite clays to obtain nanocomposites

The present study was carried out on the effect of molecular weight and polydispersity of polypropylene (PP) obtained via Ziegler‐Natta or metallocene catalysis on the formation of nanocomposites with montmorillonite and mineral and synthetic hectorite. The formation of the nanocomposites was achieved by the melt‐mix method. X‐ray diffraction, transmission electron microscopy, and analysis of mechanical properties showed that, using PP obtained via metallocene catalysis (polydispersity ～ 2), it is possible to achieve improved formation of nanocomposites compared with PP obtained via Ziegler‐Natta catalysis (polydispersity ～ 4). It was also found that the molecular weight of the PP affects the tendency toward clay exfoliation and consequently the properties of the nanocomposites. Montmorillonite type clay was evaluated at 1%, 3%, and 5% by weight in the nanocomposite. The nanocomposite with 1 wt % clay was found to have better mechanical properties compared with the nanocomposite containing 3 wt % and 5 wt %. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 698–706, 2007     

Polyolefin microstructural deconvolution methods: The good,the bad,and the ugly

The deconvolution of the molecular weight distribution (MWD) of polyolefins into Schultz–Flory most probable distributions has become the standard method to identify the number of site types on multiple-site-type olefin polymerization catalysts such as Ziegler–Natta, Phillips, and some supported metallocenes. This method has been used to quantify the effect of polymerization conditions and catalyst formulations on polyolefin MWD and olefin polymerization kinetics. Related methods have also been developed to deconvolute other polyolefin microstructure features, such as the chemical composition and comonomer sequence length distributions. In this paper, I explain the premises behind these deconvolution models and review the publications in this area, highlighting the advantages, disadvantages, and misuses of these methods. I also propose a revised formulation on how to model the MWD of polyolefins made with multiple-site-type catalysts using ratio distributions for propagation and chain transfer frequencies. The main objective of this overview article is to highlight the strengths, but also show the pitfalls, of polyolefin microstructure deconvolution methods.     

Customizing the comonomer incorporation distribution in Ziegler–Natta-based LLDPE: Harnessing the influences of the titanation temperature during catalyst synthesis and of polymerization process parameters

The microstructure of linear low-density polyethylene (LLDPE) is strongly influenced by short-chain branches (SCBs) incorporated into the polymer backbone. Varying the number, distribution, and length of SCBs allows the properties of the resulting polymer to be tailored to meet specific requirements. Using Ziegler–Natta (ZN) catalysts for synthesis has disadvantages in terms of the comonomer incorporation distribution (CID) compared to, for instance, metallocene and post–metallocene catalysts. Nevertheless, ZN catalysts continue to be widely used, as many of the new generations of catalysts are more difficult to handle and cannot match the cheap cost of ZN catalysts. To improve this aspect of ZN catalysts, we investigated the influence of catalyst titanation temperature and polymerization process parameters on the CID. Our results show that it is possible to manipulate the process parameters of the present ZN catalyst system to yield a desired comonomer amount and CID in the polymer. Varying the titanation temperature clearly influenced the titanium content of the catalyst. Molecular-weight distribution analysis and deconvolution results indicate that changes in the amounts of comonomer incorporated and in the CID are directly related to the catalyst's active site that produces the lowest-molecular-weight fraction.     

In situ synthesis of polybutene‐1/polypropylene spherical alloys within a reactor with an MgCl2‐supported Ziegler–Natta catalyst

A series of isotactic polybutene‐1/polypropylene (PB/PP) alloys with spherical morphology were prepared by MgCl₂‐supported Ziegler‐Natta catalyst with sequential two‐stage polymerization technology. The first formed PP particles were used as micro‐reactors to initiate the bulk precipitation polymerization of butene‐1 further. The porous PP particles as a hard framework may prevent the adhesion of PB particles during the bulk precipitation polymerization process. At the same time, the bulk precipitation polymerization process allows for maximization of the butene‐1 polymerization rate and simplifies the butene‐1 polymerization process considerably. Finally, spherical PB alloys with a super‐high molecular weight PB component and adjustable PP component were synthesized in situ within the reactor. The structures and properties of the PB/PP alloys were characterized by gel permeation chromatography, ¹³C nuclear magnetic resonance, Fourier transform IR, scanning electron microscopy, differential scanning calorimetry and X‐ray diffraction. The results showed that the MgCl₂‐supported Ziegler‐Natta catalyst showed relatively high stereospecificity and efficiency for both propylene and butene‐1 polymerization. The incorporation of propylene on the PB matrix affects the properties of the final products markedly. The PB/PP alloys are expected to have a broader range of applications as a new family of high performance materials. Copyright © 2012 Society of Chemical Industry     

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     

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     

Gas-phase polymerization of propylene at low reaction rates: a precise look at catalyst fragmentation

In this work, we reported the development of a mini-reactor experimental setup for synthesizing of polypropylene with heterogeneous Ziegler–Natta catalysts in gas-phase. Use of pro-activated 4th generation of Ziegler–Natta catalyst and preheated monomer feed enabled the polymerization reaction to be carried out at constant temperature. Evaluation of monomer consumption with high precision (0.01 bar pressure drop) allowed the detection of polymerization yield at low reaction rates. In this regard, polymerization yield, particle morphology and catalyst fragmentation were studied, as well. The results of melt microscopy showed that catalyst fragmentation was developed during the reaction, and was not restricted to the initial rupture of catalyst particles. The rate determination showed a peak during the polymerization (not necessarily at the initial stage). The results showed that depending on the reaction condition, this peak could be either a consequence of a major catalyst fragmentation or overheating. Low reaction yield, large fragments of catalyst and agglomeration of particles were considered as evidence of particle overheating and polymer local melting. As we imposed the results of melt microscopy for the polymerization conditions, a layer-by-layer fragmentation of the catalyst was found to be the main fragmentation process, at least at the beginning of the polymerization reaction.     

Characterization of commercial linear low‐density polyethylene by TREF‐DSC and TREF‐SEC cross‐fractionation

A new technique for characterization of linear low‐density polyethylene (LLDPE) is presented in this report. The molecular structure of two commercial LLDPEs, produced by copolymerization of ethylene with 1‐butene over a Ziegler‐Natta and a metallocene catalyst, was investigated. The LLDPE resins were fractionated by temperature rising elution fractionation (TREF), and the TREF fractions were further analyzed by size exclusion chromatography and differential scanning calorimetry (DSC) coupled with successive nucleation/annealing (SNA). The cross‐fractionation techniques provided detailed information about the molecular structure of different types of LLDPEs; of particular interest is the TREF‐SNA‐DSC cross‐fractionation which allowed a direct observation of methylene sequence distribution and thus short chain branch (SCB) distribution. TREF‐size exclusion chromatography cross‐fractionation showed that the molar mass of the Ziegler‐Natta LLDPE increased monotonically with decreasing SCB, whereas the plot of M_w vs SCB for the metallocene LLDPE showed a maximum. TREF‐SNA‐DSC cross‐fractionation clearly showed that the metallocene LLDPE only had intramolecular heterogeneity in SCB distribution, whereas the Ziegler‐Natta LLDPEs exhibited both intermolecular and intramolecular heterogeneity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 960–967, 2000     

Analysis of the effects of the polymerization route of ethylene‐propylene‐diene rubbers (EPDM) on the properties of polypropylene‐EPDM blends

A comparative study of two ethylene‐propylene‐diene rubbers (EPDM) polymerized by both conventional (Ziegler–Natta catalysts) and new techniques (metallocene catalysts) is presented. For this purpose, thermoplastic elastomers based on isotactic polypropylene (iPP) and EPDM blends at different percentages were prepared and their properties examined. In particular, the processing behavior and mechanical properties are reported. So, the flow properties analyzed by torque value, melt index, and rheological study reveal that the blends containing EPDM synthesized by metallocene catalyst present a smaller viscosity, thus offering better processing behavior. On the other hand, the mechanical properties show that metallocene EPDM rubbers give rise to more elastic materials with a higher deformation at break and resilience as well as a lower compression set. Moreover, the effectiveness of these innovative EPDM rubbers as impact modifiers for PP is demonstrated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 25–37, 2002