Millimeter‐size polyethylene hollow spheres synthesized with MgCl2‐supported Ziegler‐Natta catalyst

Polyethylene hollow spheres with diameters of 0.4–2 mm were synthesized by a two‐step slurry polymerization in a single reactor with a spherical MgCl₂‐supported Ziegler‐Natta catalyst activated by triethylaluminum, in which the first step was prepolymerization with 0.1 MPa propylene and the second step was ethylene polymerization under 0.6 MPa. The prepolymerization step was found necessary for the formation of hollow spherical particles with regular shape (perfectly spherical shape). The effects of adding small amount of propylene (propylene/ethylene < 0.1 mol/mol) in the reactor after the prepolymerization step were investigated. Average size of the polymer particles was increased, and the polymerization rate was markedly enhanced by the added propylene. Development of the particle morphology with polymerization time was also studied. The polymer particles formed by less than 20 min of ethylene polymerization showed hollow spherical morphology with thin shell layer. Most of the particles had ratio of shell thickness/particle radius smaller than 0.5. By prolonging the ethylene polymerization, the shell thickness/particle radius ratio gradually approached 1, and the central void tended to disappear. Central void in polymer particles formed from smaller catalyst particles disappeared after shorter time of polymerization than those formed from bigger catalyst particles. The shell layer of the hollow particles contained large number of macro‐, meso‐ and micro‐pores. The mesopore size distributions of four typical samples were analyzed by nitrogen adsorption–desorption experiments. A simplified multigrain model was proposed to explain the morphogenesis of the hollow spherical particles. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43207.     

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.     

MgCl2‐supported Ziegler–Natta catalyst containing dibenzoyl sulfide donor for propylene polymerization

Polypropylene (PP) was synthesized in the presence of Ziegler–Natta catalysts composed of MgCl₂‐TiCl₄‐internal donor/AlR₃‐external donor. Diisobutyl phthalate is a well‐known internal donor in current PP production. Nevertheless, phthalates are often blamed as endocrine disruptors. The objective is to find an ecofriendly internal donor producing PP with maintaining its physical properties. When using dibenzoyl sulfide, synthesized PP shows the superiority to diisobutyl phthalate in the activity of catalyst (40 vs. 22 kg PP/g catalyst), the isotacticity of polymer (99.5 vs. 98.0 wt % of heptane insolubles), and the molecular weight distribution of PP product (M_w/M_n = 4.8 vs. 4). © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40743.     

Microstructure of isotactic polypropylene obtained using Ziegler–Natta catalyst at high polymerization temperature

The microstructure of the isotactic polypropylene obtained with various MgCl₂‐supported catalyst systems at high polymerization temperature of 70–100°C is investigated by discussing the intrinsic relation between the different types of active centers and the polymerization temperatures via gel permeation chromatography, temperature rising elution fractionation, and ¹³C NMR. For the MgCl₂/TiCl₄/di‐n‐butyl phathalate‐AlEt₃/external donor and MgCl₂/TiCl₄/2,2‐diisobutyl‐1,3‐dimethoxypropane‐AlEt₃ catalyst systems, the differences in the isotactic productivity of polymers obtained at different polymerization temperatures mainly result from the variation of both the activity of the different isospecific active centers and the stability constants of the complex of catalyst/donor. The reaction rate of high isotactic active centers reaches maximum at 85–90°C, and this effect contributes to both the highest isotacticity and the narrowest molecular weight distribution. For the MgCl₂/TiCl₄/phthalate ester‐AlEt₃ catalyst system, the isotacticity of polypropylene remains approximately constant in the temperature range of experiments, which could be ascribed to elution of phthalate ester after the activation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42487.     

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.     

Kinetics of short‐duration ethylene–propylene copolymerization with MgCl2‐supported Ziegler–Natta catalyst: Differentiation of active centers on the external and internal surfaces of the catalyst particles

Ethylene–propylene copolymerization with a TiCl₄/MgCl₂ type ZN catalyst was conducted for different durations from 30 to 600 s, and changes of polymerization rate, concentration of active centers ([C^*]) and copolymer chain structure with time were traced. The copolymerization rate decayed with time, but [C^*]/[Ti] increased in the same period. This was attributed to release of more active sites through disintegration of catalyst particles by the growing polymer phase. Ethylene content of the copolymer quickly decreased in the period of 30–90 s, meaning that the active centers activated in the reaction process have stronger ability of incorporating propylene than those activated at the very beginning. The copolymer samples were fractionated into two parts, namely n‐heptane soluble fraction (random copolymer) and insoluble fraction (segmented copolymer with high ethylene content). With continuation of the copolymerization, active centers producing the random copolymer chains increased much faster than active centers producing the segmented copolymer chains, and became the dominant centers after 120 s. Consequently, proportion of the soluble fraction sharply increased with time. All these results indicate that the active centers located on the external surface of catalyst particles are highly different from those buried inside the particles. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46030.     

Mechanism of internal and external electron donor effects on propylene polymerization with MgCl2‐supported Ziegler–Natta catalyst: New evidences based on active center counting

Two TiCl₄/Di/MgCl₂ type supported Ziegler–Natta catalysts were prepared by loading dibutylphthalate or dicyclopentyldimethoxysilane (DCPDMS) (internal donor, Di) and TiCl₄ on activated δ‐MgCl₂ in sequence, and a blank catalyst was prepared by loading TiCl₄ on the same δ‐MgCl₂ without adding Di. These catalysts have similar specific surface area and pore size distribution, thus form a suitable base for comparative studies. Propylene polymerization with the catalysts was conducted in n‐heptane slurry using triethylaluminum (TEA) as cocatalyst, and the effects of Di as well as De (external donor, in this work it was DCPDMS) on the number of active centers, the distribution of active centers among three polypropylene (PP) fractions (isotactic, medium isotactic, and atactic PP chains), and chain propagation rate constants of the PP fractions were studied by counting the number of active centers in the PP fractions using a method based on selective quench‐labeling of the propagation chains by 2‐thiophenecarbonyl chloride. When De was not added in the polymerization, introducing a phthalate type Di in the catalyst evidently changed the active center distribution by enhancing the proportion of active centers producing isotactic PP (iPP) ( ), but scarcely changed reactivities of the three groups of active centers forming the three fractions. When the De was added in the polymerization system with TiCl₄/phthalate/MgCl₂ catalyst, further shifting of active center distribution in favor of took place, meanwhile reactivities of the three groups of active centers also remarkably changed in favor of . Mutual effects of these changes led to overwhelming dominance of iPP production in the TiCl₄/Di/MgCl₂–TEA/De system (Di = phthalate, De = alkoxysilane). In contrast, though using alkoxysilane as Di also caused shifting of active center distribution in favor of when De was not added, addition of alkoxysilane De caused reverse shifting of active center distribution in favor of those producing PP of lower stereoregularity. This unfavorable change largely counteracted the reactivity changes in favor of caused by the De, rendering the catalytic system rather poor isospecificity. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46605.     

Ethylene/1‐hexene copolymerization with supported Ziegler–Natta catalysts prepared by immobilizing TiCl3(OAr) onto MgCl2

Five titanium complexes TiCl₃(OAr) (Ar = C₆H₅? , 2,6‐Me₂C₆H₃? , 2,6‐i‐Pr₂C₆H₃? , 2,6‐t‐Bu₂C₆H₃? , 4‐Me‐2,6‐t‐Bu₂C₆H₃? ) were immobilized, respectively, on MgCl₂ in semibatch reaction to form supported catalysts for olefin polymerization. Comparing with the catalysts prepared by immobilizing TiCl₃(OAr) onto MgCl₂ in batch reaction, the catalysts prepared by semibatch reaction have lower titanium content and higher ArO/Ti ratio. The aryloxy‐containing catalysts studied in this work showed higher ethylene/1‐hexene copolymerization activity and higher 1‐hexene incorporation rate than the blank catalyst when activated by triisobutylaluminum. Similar effects of the aryloxy ligand were observed when the copolymerization is conducted in the presence of hydrogen. Introducing aryloxy ligand in the catalysts either by semibatch or batch reaction caused similar effects of enhancing copolymerization activity and α‐olefin incorporation rate. Mechanism of the effects of aryloxy ligand has been discussed. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41329.     

Study of propylene polymerization catalyzed by a spherical MgCl2‐supported Ziegler–Natta catalyst system: The effects of external donors

Spherical MgCl₂‐supported Ziegler–Natta catalysts containing internal donors, such as diethyl phthalate, diisobutyl phthalate, and di‐n‐octyl phthalate, have been prepared. The effects of external donors, phenyltrimethoxysilane, phenyltriethoxysilane, and diphenyldimethoxylsilane, on the propylene polymerization catalyzed by these catalysts were studied. The results indicate that the external donors not only led to an increase in the isotactic index, but also affected the morphology of resultant polymer particles. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 738–742, 2005     

Observation on different reducing power of cocatalysts on the Ziegler–Natta catalyst containing alkoxide species for ethylene polymerization

In this work, the effects of three types of cocatalyst having different alkyl groups, such as triethylaluminium (TEA), triisobutylaluminum (TiBA), and trioctylaluminium (TnOA), and their concentrations on the catalytic activity and polymer properties were investigated for the Ziegler–Natta catalyst containing alkoxide species. The drastic escalation of catalytic activity was observed when the ratio of Al/Ti was increased only for TEA because of its good diffusivity as proven by the electron spin resonance technique. Moreover, it was found that the characteristic of the alkyl group in cocatalyst affected on the chain transfer ability. The chain transfer ability of TnOA was found to be equal to the TiBA in spite of its concentration was higher. By the way, the cocatalyst types and their concentrations did not affect on the variety of active sites as seen in molecular weight distribution of polymer. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40884.     

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     

Comonomer effects in copolymerization of ethylene and 1‐hexene with MgCl2‐supported Ziegler‐Natta catalysts: New evidences from active center concentration and molecular weight distribution

In this article, comonomer effects in copolymerization of ethylene and 1‐hexene with four MgCl₂‐supported Ziegler‐Natta catalysts using either ethylene or 1‐hexene as the main monomer were investigated. It was found that no matter which monomer was used as the main monomer, the polymerization activity was significantly enhanced by introducing small amount of comonomer. In copolymerization with ethylene as the main monomer, the strength of comonomer effects was much stronger in active centers producing low‐molecular‐weight polymer than those producing high‐molecular‐weight polymer. In copolymerization with 1‐hexene as the main monomer, the number of active centers ([C*]/[Ti]) was determined, and the propagation rate constants (k_p) were calculated. Deconvolution of the polymer molecular weight distribution into Flory components were made to study the active center distribution. Introduction of small amount of ethylene caused marked increase in the number of active centers and decrease in average chain propagation rate constant. Introducing internal electron donor in the catalyst enhanced not only the number of active centers but also the chain propagation rate constant. In copolymerization of 1‐hexene with small amount of ethylene, the internal donor weakened the comonomer effects to some extent and changed the distribution of comonomer effects among different types of active centers. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41264.     

The role of two different internal donors (phthalate and 1,3‐diether) on the formation of surface structure in MgCl2‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization

The role of two different internal donors [a phthalate (diisobutylphthalate) and a 1,3‐diether (2,2‐diisobutyl‐1,3‐dimethoxypropane)] on the formation of surface structure in MgCl₂‐supported Ziegler–Natta catalysts and their catalytic performance of propylene polymerization was investigated by comparing and correlating the catalyst structures and the polymerization characteristics. In the catalyst formation, the 1,3‐diether had better affinity for the MgCl₂ surface than the phthalate and the 1,3‐diether generated the (110) surface more than the (104) surface while the phthalate generated both the (110) and (104) surfaces of MgCl₂. With both donors introduced, the (110) and (104) surfaces were generated simultaneously, although the (110) surface was dominant due to the higher affinity via the 1,3‐diether. In addition, it seemed probable that the active sites formed on the (110) plane showed isospecific characteristics in the presence of a donor while those formed on the (104) plane could be isospecific regardless of a donor. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40536.     

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     

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     

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 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 the propylene polymerization with prepolymerization at high temperature using Ziegler‐Natta catalyst

The bulk polymerization of propylene in liquid monomers with Ziegler‐Natta catalyst at 95°C is studied, using alkyl aluminum as the cocatalyst and dicyclopentyldimethoxysilane as the external donor. The highest catalyst activity is shown at the cocatalyst/Ti molar ratio of 300, which keeps relatively constant with the molar ratio increasing from 300 to 800. Besides, the catalyst activity is up to 65 kgPP/(gCat*h) in the range of cocatalyst/donor molar ratio from 12 to 16. The polymerization reaction rate curves with and without catalyst precontacting are similar, while the activity with catalyst precontacting are higher than that without precontacting. Furthermore, the kinetics of polymerization with and without prepolymerization are investigated in the range of the polymerization temperature from 70 to 95°C. It shows that at the high temperature, the polymerization rate increases with prepolymerization. Finally, the influence of prepolymerization at 95°C on the polymerization kinetics and particle properties is also described. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41816.     

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     

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