Polyolefins Journal

Polyolefins Journal

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  • Publisher: Iran Polymer and Petrochemical Institue
  • Country of publisher: iran, islamic republic of
  • Date added to EuroPub: 2019/Nov/09

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  • Language of fulltext: english

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  • Year open access content began: 2014
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This journal has '78' articles

Macromolecular non-releasing additives for safer food packaging: application to ethylene/α-olefins and propylene based polymers

Macromolecular non-releasing additives for safer food packaging: application to ethylene/α-olefins and propylene based polymers

Authors: Maria Carmela Sacchi, Simona Losio, Paola Stagnaro, Giorgio Mancini, Luca Boragno, Stefano Menichetti, Caterina Viglianisi, Sara Limbo
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Abstract

Some innovative solutions are proposed to the problem of the unavoidable physical migration of antioxidants from plastic films for packaging, in order to minimize the consequent undesirable effect of food contamination. In previous exploratory tests, phenolic antioxidant co-units were achieved and incorporated into polyethylene chain and now the work is extended to create new families of polymeric additives properly designed for specific material. An effective route was designed to synthesize the functionalized comonomer, analogues of commercial 2,6-t-butyl-4-methoxy-phenol (BHA), containing eight methylene units as spacer between the aromatic ring and the polymerizable olefinic double bond (C8). Ethylene/1-hexene/C8 terpolymers, with 1-hexene concentration in the typical range found in commercial polyethylene grades, and propylene/C8 copolymers with microstructure similar to those of commercial packaging polypropylenes were produced. A careful 13C NMR study was conducted for the precise determination of the functionalized comonomer content on all terpolymer and copolymer samples. The samples melt blended with additive-free commercial LDPE and PP matrices, individually, were analyzed in terms of thermal and thermo-oxidative stability and compared with LDPE and PP films containing the traditional BHA additive analogue. The results demonstrate that, in either way, the polymeric additives exert a very positive effect on the degradation temperature of the polymeric matrices, retarding the thermo-oxidative sequence of reaction.

Keywords: macromolecular antioxidants; blends; Polyolefins; 13C NMR; thermogravimetric analysis (TGA)
In situ stabilization of polypropylene by lignin using a Ziegler-Natta catalyst

In situ stabilization of polypropylene by lignin using a Ziegler-Natta catalyst

Authors: Maria Marques, Renato de Oliveira, Rafael Araujo, Bruno Amantes
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Abstract

A fourth-generation Ziegler-Natta catalyst was prepared to synthesize polypropylene (PP), which was stabilized by in situ polymerization employing lignin as antioxidant. The antioxidant properties of lignin were compared with those of the commercial antioxidant Irganox 1010. The presence of lignin in the reaction medium slightly decreased the catalytic activity of the reaction. The isotacticity index (I.I.) of PP synthesized with lignin (PP-lig) was not affected by the presence of the additive in the reaction medium. The thermal properties, characterized by differential scanning calorimetry, showed slightly decreased degree of crystallinity (Xc), but the melting temperature (Tm) and crystallization temperature (Tc) were not affected when compared with the neat polymer. Lignin showed good activity as a stabilizer by thermogravimetry. The initial temperature of degradation (Tonset) increased when compared to the pure PP and PP stabilized with the commercial antioxidant. The lower carbonyl index of the PP, evaluated by infrared spectroscopy (FTIR) after thermo-oxidative treatment, also revealed the stabilizing action of lignin.

Keywords: Antioxidant; polypropylene; Ziegler-Natta catalyst
Synthesis of high molecular weight polyethylene using FI catalyst

Synthesis of high molecular weight polyethylene using FI catalyst

Authors: G. Hossein Zohuri, Saman Damavandi, Saeid Ahmadjo, Reza Sandaroos, Mohammad A. Shamekhi
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Abstract

A FI Zr-based catalyst of bis[N-(3,5-dicumylsalicylidene)-2′,6′­diisopropylanilinato]zirconium(IV) dichloride was prepared and used for polymerization of ethylene. The effects of reaction conditions on the polymerization were examined in detail. The increase in ethylene pressure and rise in polymerization temperature up to 35 oC were favorable for catalyst/MAO to raise the catalytic activity as well as the viscosity-average molecular weight (Mv) of polyethylene. The activity of the catalyst was linearly increased with increasing MAO concentration and no optimum activity was observed in the range studied. Although introduction of the bulky cumyl and 2′,6′-diisopropyl alkyl substitution groups on ortho positions to the phenoxy-oxygen and on phenyl ring on the N, respectively enhanced the viscosity average molecular weight (Mv) of the obtained polymer strongly, diminished the activity of the catalyst. Neither the activity of the catalyst nor the (Mv) of the obtained polymer were sensitive to hydrogen concentration. However, higher amount of hydrogen could slightly increase the activity of the catalyst. The (Mv) of polyethylene ranged from 2.14×106 to 2.77×106 at the monomer pressure of 3 and 5 bar respectively which are much higher than that of the reported FI Zr-based catalysts.

Keywords: FI Catalyst; high molecular weight; Polyethylene; Ethylene polymerization
Storage time effect on dynamic structure of MgCl2.nEtOH adducts in heterogeneous Ziegler-Natta catalysts

Storage time effect on dynamic structure of MgCl2.nEtOH adducts in heterogeneous Ziegler-Natta catalysts

Authors: Najmeh Hadian, Shokoofeh Hakim, Mehdi Nekoomanesh, Naeimeh bahri-Laleh
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Abstract

Primary MgCl2.3.3EtOH adduct (PCT1) was prepared by melt quenching method and then submitted into a programmed thermal dealcoholation project using a fluidized bed reactor. During thermal dealcoholation program, different MgCl2.nEtOH support samples with n= 3.0, 2.7, 2.4, and 2.1 were selected and named as PCT2 to PCT5, respectively. Structural analysis of the support samples showed a significant increase in the surface area, from 7.4 m2/g to 12.8 m2/g, together with the decrease in peaks height at 2θ≈ 8.9 and 9.7˚ by moving from PCT1 to PCT5. After characterization of support samples, final catalysts were prepared by reacting these samples with TiCl4 and examined in slurry phase propylene polymerization. Prepared catalysts showed similar stereospecifities but different activities in the polymerization experiments, so that, with proceeding dealcoholation from PCT1 to PCT2 catalyst activity was reached a maximum amount of 2.9 kgPP/g Cat.h, and then by further dealcoholation, from PCT2 to PCT5, catalyst activity decreased gradually. In the last section, effect of time interval between thermal dealcoholation and catalyst preparation, which is called storage time, on the crystal and morphological characteristics of the two of the best adduct samples, namely MgCl2.2.4EtOH and MgCl2.3.0EtOH, was studied, as well. Storage time greatly affected the characteristics of the adducts together with resulted catalysts, and the best catalyst activity was achieved for the ones prepared immediately after adduct preparation.

Keywords: Ziegler-Natta; MgCl2; thermal dealcoholation; polyolefin; dynamic structure
Recent advances in the polymerization of butadiene over the last decade

Recent advances in the polymerization of butadiene over the last decade

Authors: Giovanni Ricci, Giuseppe Leone
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Abstract

The stereospecific polymerization of conjugated dienes began in 1954 with the first catalysts obtained by combining TiCl4 or TiCl3 with aluminum-alkyls, i.e. the catalytic systems previously employed for ethylene and propylene polymerizations. Subsequently, many other catalytic systems were obtained and examined by a combination of transition metal or lanthanide compounds with appropriate alkylating agents. With the advent of MAO as alkylating agent, at the beginning of the 1980s, new catalytic systems were introduced, in some cases much more active and stereospecific than those based on common aluminum-alkyls. Starting from the 2000s, in the wake of what happened in the case of mono-olefins, a new generation of catalysts based on complexes of transition ,metals and lanthanides with various ligands containing donor atoms such as P, N, O (e.g., phosphines, imines imino-pyridines, cheto-imines) has been introduced. These systems have proved particularly active and able to (provide polymers with controlled microstructure (i.e., cis-1,4; 1,2; mixed cis-1,4/1,2 with a variable 1,2 content ,from several types of 1,3-dienes, permitting indeed to establish new correlations between the catalyst structure the monomer structure and the polymer microstructure, and to improve our knowledge on the polymerization mechanism of 1,3-dienes. This paper provides an exhaustive overview of the latest developments in the field of stereospecific polymerization of 1,3-butadiene.

Keywords: butadiene; catalysts; stereospecific polymerization; polybutadiene
Propene-cycloolefin polymerization

Propene-cycloolefin polymerization

Authors: Laura Boggioni, Incoronata Tritto
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Abstract

Highly active metallocenes and other single site catalysts have opened up the possibility of polymerizing cycloolefins such as norbornene (N) or of copolymerizing them with ethene (E) or propene (P). The polymers obtained show exciting structures and properties. E-N copolymers are industrially produced materials, with variable and high glass transitions depending on the wide range of their microstructures. By realizing the possibility in great variety of stereoregularity of propene and norbornene units and the difference in comonomer distribution, P-N copolymers were expected to have fine tuned microstructures and properties. Moreover, P-N copolymers should be characterized by higher Tg-values than E-N copolymers with the same norbornene content and molar mass. A review of the state of the art of P-N copolymerization by ansa-metallocenes of C2 symmetry, namely rac-Et(Ind)2ZrCl2 (I-I) and rac-Me2Si(Ind)2ZrCl2 (I-II), and rac-Me2Si(2-Me-Ind)2ZrCl2 (I-III), and of catalysts of Cs symmetry, namely (tBuNSiMe2Flu)TiMe2 (IV-I) and derivatives, is given here. Special emphasis is given to microstructural studies of P-N copolymers, including stereo- and regioregularity of propene units as well as of comonomer distribution, stereoregularity of norbornene units, and the structure of chain end-groups. This information allows us to find a rationale for the catalytic activities and the copolymer properties.

Keywords: Propene; norbornene; metallocene catalysts; cycloolefin copolymers; microstructure
Modelling the catalyst fragmentation pattern in relation to molecular properties and particle overheating in olefin polymerization

Modelling the catalyst fragmentation pattern in relation to molecular properties and particle overheating in olefin polymerization

Authors: Mohsen Najafi, Mahmoud Parvazinia, Mir Hamid Reza Ghoreishy
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Abstract

A two-dimensional single particle finite element model was used to examine the effects of particle fragmental pattern on the average molecular weights, polymerization rate and particle overheating in heterogeneous Ziegler-Natta olefin polymerization. A two-site catalyst kinetic mechanism was employed together with a dynamic two-dimensional molecular species in diffusion-reaction equation. The initial catalyst active sites distribution was assumed to be uniform, while the monomer diffusion coefficient was considered to be different inside the fragments and cracks. In other words, the cracks were distinguished from fragments with higher monomer diffusion coefficient. To model the particle temperature a lumped heat transfer model was used. The fragmentation pattern was considered to remain unchanged during the polymerization. A Galerkin finite element method was used to solve the resulting two-dimensional (2-D) moving boundary value, diffusion-reaction problem. A two-dimensional polymeric flow model (PFM) was implemented on the finite element meshes. The simulation results showed that the fragmentation pattern had effects on the molecular properties, reaction rate and the particle temperature at early stages of polymerization.

Keywords: particle overheating; finite element method; modelling; particle growth; polyolefin
Tuning the short chain branch distribution of ethylene and 1-hexene copolymers by SiO2-supported silyl chromate catalyst with different Al-alkyl co-catalysts

Tuning the short chain branch distribution of ethylene and 1-hexene copolymers by SiO2-supported silyl chromate catalyst with different Al-alkyl co-catalysts

Authors: Ning ZHAO, Ruihua Cheng, Qi Dong, Xuelian He, Zhen Liu, Shiliang Zhang, Minoru Terano, Boping Liu
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Abstract

SiO2-supported silyl chromate catalyst is an important industrial catalyst for production of high grade HDPE pipe materials. The control of the short chain branch (SCB) distribution using this catalyst system is still a great challenge. In this work, ethylene and 1-hexene copolymers were synthesized using SiO2-supported silyl chromate catalyst combined with triisobutylaluminium (TIBA), triethylaluminium (TEA) and mixed TIBA/TEA at molar ratio 1:1 (TIBA/TEA/1:1) as three different Al-alkyl co-catalysts.The temperature rising elution fractionation (TREF) and successive self-nucleation and annealing (SSA, by DSC) methods were combined to analyze the short chain branch distribution (SCBD) of these ethylene/1-hexene copolymers. The results showed that different types of co-catalyst had a great influence on SCBD of ethylene/1-hexene copolymers. The copolymer produced with TIBA showed better SCBD than the copolymer produced with TEA, and the copolymer produced with TIBA/ TEA/1:1 showed a SCBD in between those with TIBA and TEA.

Keywords: ethylene/1-hexene copolymerization; Al-alkyl co-catalyst; polymerization kinetics; SiO2-supported silyl chromate catalyst; short chain branch distribution
Dissymmetric dinuclear transition metal complexes as dual site catalysts for the polymerization of ethylene

Dissymmetric dinuclear transition metal complexes as dual site catalysts for the polymerization of ethylene

Authors: Haif Alshammari, Helmut G. Alt
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Abstract

A series of dissymmetric dinuclear complexes were synthesized, as dual site catalysts in ethylene polymerization, by coupling the allylated a-diimine complexes of the metals Ti, Zr, V, Ni and Pd with the ansa-zirconocene complex [C5H4-SiH(Me)-C5H4]ZrCl2 possessing a hydride silane moiety. The different stages of syntheses included the formation of bis(cyclopentadienide)methyl silane which was utilized to prepare the silyl-bridged zirconocene complexes. The dinuclear complexes were prepared by mixing the latter complexes with allylated alpha-diimine via a hydrosilylation reaction using the Karstedt catalyst, platinum (0)1,3 divinyl-1,1,3,3,-tetramethyldisiloxane to react at room temperature for 40 h. These dinuclear complexes were activated with methylaluminoxane (MAO) and tested for the polymerization of ethylene. The dinuclear catalysts showed various activities depending on the nature of the metals and produced polyethylenes with broad or bimodal molecular weight distributions. The trend in polymerization activities was: Ni>Pd>V>Zr>Ti. The ethylene polymerization activities of the dinuclear catalysts were almost double the activities of their analogous alpha-diimine precursors.

Keywords: dissymmetric dinuclear complexes; Ti, Zr, V, Ni, Pd; Dual site ethylene polymerization catalysts; Bimodal resins
The role of 1-hexene comonomer content in thermal behavior of medium density polyethylene (MDPE) synthesized using Phillips catalyst

The role of 1-hexene comonomer content in thermal behavior of medium density polyethylene (MDPE) synthesized using Phillips catalyst

Authors: Abbas Kebritchi, Mehdi Nekoomanesh, Fereidoon Mohammadi, Hossein-Ali Khonakdar
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Abstract

In this work, the role of comonomer content of 1-hexene-medium density polyethylene (MDPE) copolymer, synthesized using Phillips catalyst, on thermal behavior parameters such as: crystallization, melting temperature and thermal degradation was investigated in detail. The copolymer was fractionated to homogenous short-chain branching (SCB) fractions by "preparative temperature rising elution fractionation" (P-TREF) method and then it was subjected to thermal analyses. A broad chemical composition distribution (CCD) in terms of SCB content and molecular weight (Mw) was observed by P-TREF and gel permeation chromatography (GPC), respectively. Based on P-TREF results, a parabolic relationship between methylene sequence length (MSL) and elution temperature (ET) was presented. Differential scanning calorimetry (DSC) showed distinct, well-defined melting peaks over a 22 °C temperature range for SCB contents of about 3-12 (br/1000 C). The variations in physical characteristics such as melting temperature (Tm), crystallinity (Xc), crystallization temperature (Tc) and lamellae thickness (Lc) against SCB content were correlated. Thermogravimetric analysis (TGA) suggested linear relationships between the temperature at maximum degradation rate (Tmax) as well as the degradation initiation temperature (T5%) versus SCB content. Moreover, the TGA curves exhibited distinct differences at both initiation and propagation stages of thermal degradation at dissimilar comonomer contents.

Keywords: ethylene/1-hexene copolymer; short-chain branching (SCB); Thermal degradation; phillips catalyst; medium density polyethylene (MDPE)
Amoco CD commercial polypropylene catalyst tailor-made for the Amoco-Chisso gas phase process

Amoco CD commercial polypropylene catalyst tailor-made for the Amoco-Chisso gas phase process

Authors: Gregory G. Arzoumanidis
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Abstract

The commercial profile of the Amoco CD MgCl2 supported polypropylene catalyst is presented. The development, the unique method of preparation/production, with emphasis on particle morphology, and the parameters affecting particle size (PS), particle size distribution (PSD), and particle shape are discussed in detail. The outstanding performance of the catalyst, tailoredmade for the Amoco-Chisso gas phase process, is attributable to synergistic effects, originating from catalyst and process design factors. Catalyst median particle size (d50) may be controlled in the 7-100 microns range. Parameters affecting PS and PSD during catalyst support preparation include: agitation speed, temperature, organic reagent to Mg ratios, morphology controlling agents, and deliberate spiking of the aromatic solvent used with appropriate contaminants. Particle shape variation between the cubic and spheroidal is affected by the types of reagents used, the ratios of these reagents to Mg, the time/temperature profile of the procedure, and the sequence of reagent addition during catalyst support preparation. Catalyst activation takes place in several steps by thermal treatment of the support with TiCl4/toluene solutions. Cost-effective TiCl4/toluene reuse system from the activation streams has been put in place to reduce waste material considerably. There is an optimum temperature of activation close to 120˚C. The progress of activation as well as catalyst quality may be monitored by IR spectroscopy, expressed in easily identifiable IR fingerprint patterns, which correlate well with the catalyst performance. More recently a new concept of supported catalysts based on the CD technology has been developed. It features organometallic complexes instead of just TiCl4 as the polymerization active centers. The new catalysts show improved performance and advantageous polymer product properties. We suggest that the newly invented organometallic complexes may open a new era in polyolefin catalysis, including polyethylene copolymers. The success of the CD and Amoco-Chisso process is illustrated by the two dozen commercial plants worldwide that use the technology, and the recent licensing advances by Ineos, the successor of Amoco, for this polypropylene technology.

Keywords: Amoco CD polypropylene catalyst; gas phase; Amoco-Chisso process
Testing DFT ability to predict the stereoselectivity of group 4 metallocenes in propylene polymerization

Testing DFT ability to predict the stereoselectivity of group 4 metallocenes in propylene polymerization

Authors: Naeimeh bahri-Laleh, Laura Falivene, Luigi Cavallo
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Abstract

In this study we have tested the ability of a standard DFT computational protocol to reproduce the experimentally obtained stereoselectivity of 26 different C2-symmetric zirconocene catalysts active in propylene polymerization. The catalysts were chosen for their relevance in metallocene catalyzed polymerization of propylene. To this end, primary insertion of both si- and re-propylene enantiofaces into the Zr-CH2-CH(CH3)2 bond was considered to simulate the growing chains step. The energy difference between these two transition states, ΔEre-si, was taken as a measure of the stereoselectivity (pentad: mmmm%) of different catalysts. The results clearly indicated that there was a good agreement between ΔEre-si and the mmmm% values, so that greater ΔEre-si could correspond to higher mmmm%. A model was fitted to the experimentally obtained mmmm% against theoretical ΔEre-si. The coefficient of determination (R2) of the resultant plot was 0.9793, which indicated a good accuracy of the model. Finally, to quantify the steric role of the studied ligands in the observed stereoselectivity, the analysis of the buried volume (VBur) and of the steric maps was performed for two representative complexes. The images revealed that a greater asymmetric localization of the %VBur around the metal center led to a higher mmmm% in the resultant polymer.

Keywords: metallocene catalysts; DFT; Molecular simulation; Setereoselective polymerization; Isotactic polypropylene
Discovery and development of metallocene-based polyolefins with special properties

Discovery and development of metallocene-based polyolefins with special properties

Authors: Walter Kaminsky, Mercia Fernandes
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Abstract

Beside Ziegler-Natta and Phillips catalysts the development of methylaluminoxane (MAO) as cocatalyst in combination with metallocenes or other transition metal complexes for the polymerization of olefins has widely increased the possibilities in controlling the polymer composition, polymer structure, tacticity and special properties with high precision. These catalysts allow the synthesis of isotactic, isoblock, syndiotactic, stereoblockor atactic polymers, as well as polyolefin composite materials with superior properties such as film clarity, tensile strength and lower content of extractables. Metallocene and other single site catalysts are able to copolymerize ethene and propene with short and long chained a-olefins, cyclic olefins, or polar vinyl monomers such as ethers, alcohols or esters, especially, if the polar monomers are protected by aluminum alkyls. Different vinyl ethers such as vinyl-ethyl ether, vinyl-propyl ether, vinyl-hexyl ether, and 2,7-octadienyl methyl ether (MODE) were copolymerized with olefins using triisobutyl aluminum as protecting agents. Polar monomers could be incorporated into the polymer chain by up to 16 mol%. Such copolymers show better gas barrier and surface properties, as well as solvent resistance and they are suitable for blends of polyolefins with polyethers and other polar polymers because of an excellent adhesion of the two polymers.

Keywords: Methylaluminoxane; metallocene catalysts; olefin copolymerization; polar monomers; vinyl ethers
Intelligent catalysts for ethylene oligomerization and polymerization

Intelligent catalysts for ethylene oligomerization and polymerization

Authors: Helmut G. Alt
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Abstract

Ethylene polymerization catalysts became available in an enormous variety. The challenge in this research is to find catalysts that are able to connect ethylene molecules in such a way that not only linear chains are produced but variations like branched materials that possess very interesting mechanical properties like linear low density polyethylene (LLDPE). In this contribution, three different types of catalysts are presented that are able to do not only one job at a time but three. These are “intelligent catalysts”. Catalysts of type 1 are homogeneous metallocene complexes that can be activated with methylaluminoxane (MAO).With ethylene they produce their own support and they become heterogeneous catalysts (self-immobilization) and they prevent fouling in polymerization reactors. The produced resin has evenly distributed ethyl branches (without a comonomer) with unique properties and the MAO that is necessary in the activation step can be recycled. Catalysts of type 2 are dinuclear complexes with two different active sites. One centre can oligomerize ethylene and the other one can copolymerize the in statu nascendi produced oligomers with ethylene to give branched LLDPE (a molecule as the smallest reactor for LLDPE) and/or bimodal resins. Catalysts of type 3 are MAO activated iron di (imino) pyridine complexes that are able to oligomerize ethylene to give not only oligomers with even numbered carbon atoms but also odd numbered ones. In this reaction, one catalyst does three jobs at a time: oligomerization, isomerization and metathesis of ethylene.

Keywords: multi talented catalysts; oligomerization; polymerization; metathesis of ethylene; metallocene catalysts; di(imino) pyridine catalysis
Kinetics of ethylene polymerization over titanium-magnesium catalysts: The reasons for the observed second order of polymerization rate with respect to ethylene

Kinetics of ethylene polymerization over titanium-magnesium catalysts: The reasons for the observed second order of polymerization rate with respect to ethylene

Authors: Mikhail A. Matsko, Vladimir Aleksandrovich Zakharov, Marina I. Nikolaeva, Tatiana B. Mikenas
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Abstract

The data on the effect of ethylene concentration on polymerization rate for several modifications of modern highly active titanium–magnesium catalysts TiCl4/MgCl2 are presented. These catalysts differ in titanium content and conditions of support preparation, activities, and the shape of kinetic curves. It is found that the observed order of polymerization rate with respect to ethylene in the range of ethylene pressures of 0.5–6 bar is 1.8-2.1 for all catalysts used (polymerization at 80°C, AlEt3 used as a cocatalyst). When AlEt3 was replaced with Al(i-Bu)3, the reaction order decreased to 1.3-1.4. In order to elucidate the possible reasons for the observed high order with respect to ethylene, we analyzed the data on the effect of monomer concentration on the molecular weight of polyethylene. The results gave grounds for suggesting that the observed order with respect to monomer is attributable to the effect of ethylene concentration on the number of active sites. The possible reaction scheme explaining the nonlinear dependence of the polymerization rate on monomer concentration was proposed based on these data.

Keywords: polyethylene (PE); polymerization kinetics; Ziegler-Natta polymerization; molecular weight distribution / molar mass distribution

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