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     

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.     

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.     

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

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

Study of the morphology and kinetics of novel Ziegler–Natta catalysts for propylene polymerization

The morphological and kinetic characteristics of novel Ziegler–Natta catalysts were studied. Catalysts were prepared by Borealis Polymers Oy using a new synthesis technique (emulsion technology). Video microscopy was used to study the growth of single catalyst particles during polymerization in the gas and liquid phases. The distribution of single particle activity was very narrow in the catalyst without external support and was rather broad in the the silica‐supported catalyst. Video microscopy of molten polymer particles allowed observation of the process and degree of fragmentation of the catalyst particles. A correlation between the activation period during the initial stage of polymerization and catalyst fragmentation was found. Fragmentation was faster and more uniform with the catalyst without external support than with the silica‐supported catalyst. Scanning electron microscopy provided information on morphology evolution and shape replication of the catalyst particles. With the catalyst without external support, good shape replication was observed, and compact and spherical particles were formed. With the silica‐supported catalyst, shape replication was poor, and nonspherical porous polymer particle were formed. Modeling of the kinetics of propylene polymerization was done using a simple three‐step reaction scheme neglecting mass and heat transport effects. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2191–2200, 2005     

Solubility of 1‐hexene in LLDPE synthesized by (2‐MeInd)2ZrCl2/MAO and by Mg(OEt)2/DIBP/TiCl4–TEA

The solubility of 1‐hexene was measured for linear low‐density polyethylenes (LLDPEs) produced over a heterogeneous Ziegler–Natta catalyst, Mg(OEt)₂/DIBP/TiCl₄–TEA (ZN), and over a homogeneous metallocene catalyst, (2‐MeInd)_zZrCl₂–MAO (MT). The 1‐hexene solubility in LLDPEs was well represented by the Flory–Huggins equation with a constant value of χ. ZN–LLDPEs dissolved a larger amount of 1‐hexene and thus showed a lower value of χ compared to MT–LLDPEs. The Flory–Huggins interaction parameter χ, or the solubility of 1‐hexene at a given temperature and pressure, was suggested as a sensitive measure for the composition distribution of LLDPEs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1566–1571, 2002; DOI 10.1002/app.10418     

Copolymerization of propylene with 1‐octene catalyzed by MgCl2/TiCl4/diether catalyst

MgCl₂/TiCl₄/diether is a fifth‐generation Ziegler–Natta catalyst for the commercial polymerization of propylene. The outstanding features of this catalyst are the high activity and high isotacticity for propylene polymerization without using an external electron donor. In this study, we explored the copolymerization of propylene and 1‐octene with MgCl₂/TiCl₄/diether catalyst. It was found that MgCl₂/TiCl₄/diether catalyst showed higher polymerization activity and led to greater 1‐octene content incorporation, compared with a fourth‐generation Ziegler–Natta catalyst (MgCl₂/TiCl₄/diester). With an increase in 1‐octene incorporation in polypropylene chains, the melting temperature, glass transition temperature and crystallinity of the copolymers decreased distinctly. The microstructures of the copolymers were characterized using ¹³C NMR spectroscopy, and the copolymer compositions and number‐average sequence lengths were calculated from the dyad concentration and distribution. This result is very important for the in‐reactor polyolefin alloying process, especially for the case of a single catalyst and two‐step (or two‐reactor) process. Copyright © 2011 Society of Chemical Industry     

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     

Kinetics of short‐duration ethylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: Two‐stage initiation evidenced by changes in active center concentration

The kinetics of ethylene polymerization with a TiCl₄/MgCl₂‐type Ziegler–Natta catalyst was studied. Changes in polymerization activity and concentration of active centers ([C*]) in the first 5 min were determined. Initiation of the active centers was found to proceed in two stages. In the first stage, [C*]/[Ti] quickly rose to about 1% in less than 30 s and then remained stable in the subsequent 60 s. Then the [C*]/[Ti] value started to increase again, forming the second buildup stage. The polymerization activity was found to change roughly in parallel with the change in [C*]/[Ti]. Changes in the polymer/catalyst particle morphology and polymer molecular weight distribution with polymerization time were studied. A mechanistic model was proposed to explain the two‐stage kinetics: initiation of active sites on the outer surface of catalyst particles takes place in the first stage, and initiation of active sites buried inside the particles takes place in the second stage. These buried sites are released when the catalyst particles are fragmented by the expanding polymer phase. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45187.     

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

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

Effects of chemical structure of phenolic antioxidants on Ziegler–Natta catalyst performance during propylene polymerization

Present work studied the synthesis of in-reactor stabilization of polypropylene via introducing antioxidant into polymerization media. Special attention was dedicated to assess the efficiency of antioxidant in catalyst deactivation. Three different types of antioxidants (Irganox 1076, Irganox 1010 and Irganox 1330) which contain ester and/or phenolic OH functional groups were chosen to investigate their impact on Ziegler–Natta catalyst performance during slurry propylene polymerization. Our Results indicated that not only phenolic OH groups but also esteric bond of antioxidants are capable of interacting with active center of catalyst and consequently decreasing the catalyst activity. Our propylene polymerization results showed that determining factors such as antioxidant chemical structures and its steric hindrance effect and the number of functional groups (phenolic and esteric groups) affected on the Ziegler–Natta catalyst performance. Therefore, effects of these three types of antioxidants on polymer characteristics such as particle size distribution, morphology, T _m , T _c , X _c , and isotacticity were evaluated. Morphological analysis using scanning electron microscopy (SEM) showed that introducing antioxidant during propylene polymerization did not destroy the spherical morphology of the polypropylene particles. Conclusively, due to the negative effect of esteric bond of antioxidant on Ziegler–Natta catalyst performance, the use of antioxidant without ester groups (Irganox 1330) is more recommended during propylene polymerization.     

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     

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.     

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     

Preparation of ultra‐high‐molecular‐weight polyethylene and its morphological study with a heterogeneous Ziegler–Natta catalyst

Ultra‐high‐molecular‐weight polyethylene (PE) with viscosity‐average molecular weight (M_v) of 3.1 × 10⁶ to 5.2 × 10⁶ was prepared with a heterogeneous Ziegler–Natta MgCl₂ (ethoxide type)/TiCl₄/triethylaluminum catalyst system under controlled conditions. The optimum activity of the catalyst was obtained at a [Al]/[Ti] molar ratio of 61 : 1 and a polymerization temperature of 60°C, whereas the activity of the catalyst increased with monomer pressure and decreased with hydrogen concentration. The titanium content of the catalyst was 2.4 wt %. The rate/time profile of the catalyst was a decay type with a short acceleration period. M_v of the PE obtained decreased with increasing hydrogen concentration and polymerization temperature. The effect of stirrer speeds from 100 to 400 rpm did not so much affect the catalyst activity; however, dramatic effects were observed on the morphology of the polymer particles obtained. A stirrer speed of 200 rpm produced PE with a uniform globulelike morphological growth on the polymer particles. The particle size distributions of the polymer samples were determined and were between 14 and 67 μm. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Novel magnetic polyethylene nanocomposites produced by supported nanometre magnetic Ziegler–Natta catalyst

This paper describes the preparation of novel magnetic polyethylene nanocomposites using a nanometre magnetic Ziegler–Natta catalyst. It was found that novel magnetic polyethylene nanocomposites can be obtained according to the following four steps: (1) preparation of nanometre magnetic particles; (2) reaction between AlR₃ and hydroxyls on the surface of nanometre magnetic particles to form anchor points  AlR₂; (3) addition of TiCl₄, Ti being coordinated to anchor points on the surface of nanometre magnetic particles to form polymerization active centres; (4) ethylene polymerization being carried out in situ on the surface of the nanometre magnetic particles to produce novel magnetic polyethylene nanocomposites. It is found that the activity of ethylene polymerization is essentially unaffected by polymerization temperature and polymerization time. © 2000 Society of Chemical Industry     

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.     

Polymerization of propylene using the high‐activity Ziegler–Natta catalyst system SiO2/MgCl2 (ethoxide type)/TiCl4/Di‐n‐butyl phthalate/triethylaluminum/dimethoxy methyl cyclohexyl silane

The bisupported Ziegler–Natta catalyst system SiO₂/MgCl₂ (ethoxide type)/TiCl₄/di‐n‐butyl phthalate/triethylaluminum (TEA)/dimethoxy methyl cyclohexyl silane (DMMCHS) was prepared. TEA and di‐n‐butyl phthalate were used as a cocatalyst and an internal donor, respectively. DMMCHS was used as an external donor. The slurry polymerization of propylene was studied with the catalyst system in n‐heptane from 45 to 70°C. The effects of the TEA and H₂ concentrations, temperature, and monomer pressure on the polymerization were investigated. The optimum productivity was obtained at [Al]/[DMMCHS]/[Ti] = 61.7:6.2:1 (mol/mol/mol). The highest activity of the catalyst was obtained at 60°C. Increasing the H₂ concentration to 100 mL/L increased the productivity of the catalyst, but a further increase in H₂ reduced the activity of the catalyst. Increasing the propylene pressure from 1 to 7 bar significantly increased the polymer yield. The isotacticity index (II) decreased with increasing TEA, but the H₂ concentration, temperature, and monomer pressure did not have a significant effect on the II value. The viscosity‐average molecular weight decreased with increasing temperature and with the addition of H₂. Three catalysts with different Mg/Si molar ratios were studied under the optimum conditions. The catalyst with a Mg/Si molar ratio of approximately 0.93 showed the highest activity. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1177–1181, 2003     

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     

An experimental study on the early stages of gas‐phase olefin polymerizations using supported Ziegler–Natta and metallocene catalysts

The initial stages of gas‐phase polymerizations of propylene and ethylene are analyzed using a fixed bed stopped flow reactor. The very early development of particle morphology and polymer properties is analyzed for three different commercial catalyst systems: MgCl₂‐ and SiO₂‐supported Ziegler–Natta and SiO₂‐supported metallocene. It is shown that, depending on the operating conditions, distinct nonuniform catalyst fragmentation patterns can develop, confirming different scenarios described by published fragmentation models. In addition, it is shown that the molecular weight distributions and polymer yields obtained during the very early stages of the polymerization suggest the existence of significant temperature gradients inside the growing polymer particles. Finally, it is shown that the ratio of catalyst to glass beads in the bed can have a pronounced effect on the evolution of the polymerization reaction. This can be interpreted in terms of the significant temperature difference between the polymer particles and the gaseous monomer stream. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers