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1.
Y. V. Kissin R. I. Mink T. E. Nowlin A. J. Brandolini 《Journal of polymer science. Part A, Polymer chemistry》1999,37(23):4281-4294
Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit a number of features that differentiate them from polymerization reactions of α olefins: (1) a relatively low ethylene reactivity, (2) markedly higher polymerization rates in the presence of α olefins, (3) a high reaction order with respect to ethylene concentration, and (4) a strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions1 provided the basis for a new kinetic scheme that postulates the equilibrium formation of Ti C2H5 species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts several new features of ethylene polymerization reactions, one being that chain initiation via insertion of any α-olefin molecule into the Ti H bond should proceed with an increased probability compared to that via ethylene insertion into the same bond. As a result, a significant fraction of ethylene/α-olefin copolymer chains should contain α-olefin units as the starting units. This article provides experimental data supporting this prediction on the basis of both a detailed structural analysis of co-oligomers formed in ethylene/1-pentene and ethylene/4-methyl-1-pentene copolymerization reactions and a spectroscopic analysis of chain ends in the copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4281–4294, 1999 相似文献
2.
Anatoli Lisovskii Michael Shuster Michael Gishvoliner Gershon Lidor Moris S. Eisen 《应用有机金属化学》1998,12(6):401-408
The polymerization of propylene using a mixture of racemic metallocenes and Ziegler–Natta catalysts was investigated. The polypropylene was obtained as a mixture of a fine powder and beads, with the powder being absorbed partially on the beads. The relative amount of the powder can be controlled by the concentration of the metallocene. The compatibility between the components of the mixed catalytic systems and the effect of the components on the rate of polymerization and on the properties of the new polymers were studied. The metallocene system dramatically affects the melt viscosity, isotacticity and molecular weight of the polymers. The two catalytic systems are able to act jointly, producing different polymers, for which separate melting and crystallization temperatures are obtained. © 1998 John Wiley & Sons, Ltd. 相似文献
3.
James C. W. Chien Takashi Nozaki 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):227-237
Homopolymerization of ethylene and 1-hexene and their copolymerizations were compared to investigate the influence of α-olefin on the enhancement of ethylene polymerization rate (Rp), which is often referred to as the “comonomer” effect. With the two homogeneous Ziegler–Natta catalysts, Et[Ind]2ZrCl2/MAO and (π-C5H5)2ZrCl2/MAO (MAO = methylaluminoxane), hexene causes reduction of Rp—in other words a negative “comonomer” effect. In the case of the high activity MgCl2 supported TiCl3 catalysts there is a slight positive “comonomer” effect; the Rp increases by 25 to 70% with the addition of 15 mol % of hexene. The “comonomer” effects in there catalyst systems are much smaller than that observed for the classical TiCl3 catalyst. © 1993 John Wiley & Sons, Inc. 相似文献
4.
Y. V. Kissin R. I. Mink T. E. Nowlin 《Journal of polymer science. Part A, Polymer chemistry》1999,37(23):4255-4272
Kinetics of ethylene homopolymerization reactions and ethylene/1-hexene copolymerization reactions using a supported Ziegler–Natta catalyst was carried out over a broad range of reaction conditions. The kinetic data were analyzed using a concept of multicenter catalysis with different centers that respond differently to changes in reaction parameters. The catalyst contains five types of active centers that differ in the molecular weights of material they produce and in their copolymerization ability. In ethylene homopolymerization reactions, each active center has a high reaction order with respect to ethylene concentration, close to the second order. In ethylene/α-olefin copolymerization reactions, the centers that have poor copolymerization ability retain this high reaction order, whereas the centers that have good copolymerization ability change the reaction order to the first order. Hydrogen depresses activity of each type of center in the homopolymerization reactions in a reversible manner; however, the centers that copolymerize ethylene and α-olefins well are not depressed if an α-olefin is present in the reaction medium. Introduction of an α-olefin significantly increases activity of those centers, which are effective in copolymerizing it with ethylene but does not affect the centers that copolymerize ethylene and α-olefins poorly. To explain these kinetic features, a new reaction scheme is proposed. It is based on a hypothesis that the Ti—C2H5 bond in active centers has low reactivity due to the equilibrium formation of a Ti—C2H5 species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4255–4272, 1999 相似文献
5.
Effects of Alterations to Ziegler–Natta Catalysts on Kinetics and Comonomer (1‐Butene) Incorporation
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Various MgCl2‐supported Ziegler–Natta (ZN) catalysts are synthesized with the intention to influence polymerization performance and 1‐butene incorporation in an ethylene copolymer. Modifications are introduced during different steps in the synthesis process, namely support preparation, titanation, and catalyst workup. While multiple different effects are observed upon modification, heat treatment during titanation shows the greatest impact. Increasing the heat‐treatment temperature increases polymerization activity. More importantly, the 1‐butene distribution can be shifted toward a more homogeneous profile. The amount of 1‐butene incorporated is similar to both for short‐ and for very long‐chain molecules. This behavior has so far been known only from metallocene‐based polyethylene and suggests that active sites are distributed more homogeneously in the ZN catalyst.
6.
Yury V. Kissin Robert I. Mink Anita J. Brandolini Thomas E. Nowlin 《Journal of polymer science. Part A, Polymer chemistry》2009,47(13):3271-3285
Combinations of dialkylaluminum chlorides and dialkylmagnesium compounds, when used at molar [AlR2Cl]:[MgR2] ratios ≥ 2, act as universal cocatalysts for all three presently known types of alkene polymerization catalysts—Ziegler–Natta, metallocene, and post‐metallocene. When these cocatalysts are used with supported Ti‐based Ziegler–Natta catalysts, they produce catalyst systems which are 1.5–2 times more active than the systems utilizing AlR3 compounds as cocatalysts. Combinations of AlR2Cl/MgR2 cocatalysts and various metallocene complexes produce single‐center catalyst systems similar to those formed in the presence of MAO. The same cocatalysts activate numerous post‐metallocene Ti complexes containing bidentate ligands of a different nature and produce multicenter systems of very high activity. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3271–3285, 2009 相似文献
7.
Y. V. Kissin A. J. Brandolini 《Journal of polymer science. Part A, Polymer chemistry》1999,37(23):4273-4280
Ethylene polymerization reactions with many Ziegler–Natta catalysts exhibit several features which differentiate them from polymerization reactions of α-olefins: a relatively low ethylene reactivity, higher polymerization rates in the presence of α-olefins, a high reaction order with respect to ethylene concentration, and strong reversible rate depression in the presence of hydrogen. A detailed kinetic analysis of ethylene polymerization reactions (see ref. 1 ) provided the basis for a new reaction scheme which explains all these features by postulating the equilibrium formation of a Ti C2H5 species with the H atom in the methyl group β-agostically coordinated to the Ti atom in an active center. This mechanism predicts that the β-agostically stabilized Ti C2H5 groups can decompose in the β-hydride elimination reaction with expulsion of ethylene and the formation of a Ti H bond even in the absence of hydrogen in the reaction medium. If D2 is used as a chain transfer agent instead of H2, the mechanism predicts the formation of deuterated ethylene molecules, which copolymerize with protioethylene. To prove this prediction, several ethylene homopolymerization reactions were carried out with a supported Ziegler–Natta titanium-based catalyst in the presence of large amounts of D2. Analysis of gaseous reaction products and polymers confirmed the formation of several types of deuterated ethylene molecules and protio/deuterioethylene copolymers, respectively. In contrast, a metallocene catalyst, Cp2ZrCl2 MAO, does not exhibit these kinetic features. In the presence of deuterium, it produces only DCH2 CH2 (CH2 CH2)x CH2 CH2D molecules. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4273–4280, 1999 相似文献
8.
L. Sun C. C. Hsu D. W. Bacon 《Journal of polymer science. Part A, Polymer chemistry》1994,32(11):2127-2134
Polymer-supported Ziegler–Natta catalysts based on various polymer carriers were synthesized by different methods, including (1) loading TiCl4 directly onto the polymer supports; (2) loading TiCl4 onto the polymer supports modified by magnesium chloride (MgCl2); (3) loading TiCl4 onto the polymer supports modified by Grignard reagent (RMgCl); and (4) loading TiCl4 onto the polymer supports modified by magnesium alkyls (MgR2). The activity and kinetic features of the catalysts for ethylene polymerization were examined. Among the combinations tested, the best was found to be TiCl4/n-Bu2Mg.Et3Al/poly(ethylene-co-acrylic acid) (92:8), which produced a catalyst of very high activity for ethylene polymerization. © 1994 John Wiley & Sons, Inc. 相似文献
9.
Yury V. Kissin Robert I. Mink 《Journal of polymer science. Part A, Polymer chemistry》2010,48(19):4219-4229
This article describes ethylene/1‐hexene copolymerization reactions with a supported titanium‐based, multicenter Ziegler‐Natta catalyst. The catalyst was modified by pretreating its solid precursor with AlEt2Cl and with similar organoaluminum chlorides, Al2Et3Cl3, AlEtCl2, and AlMe2Cl. Testing of the untreated and the pretreated catalysts in copolymerization reactions under standard reaction conditions demonstrated that the modifying agents produce two changes in the catalyst. First, the pretreatment significantly reduces the reactivity of active centers that produce high molecular weight, highly crystalline copolymer components with a low 1‐hexene content. Second, the pretreatment noticeably increases the reactivity of active centers that produce low molecular weight copolymer components with a high 1‐hexene content. The first effect is caused by Lewis acid‐base interactions of the modifiers with the active centers, whereas the second (activating) effect is due to the removal of catalyst poisons (organosilicon compounds generated in the process of the catalyst synthesis) by AlEt2Cl. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4219–4229, 2010 相似文献
10.
Monomer-isomerization copolymerizations of styrene (St) and cis-2-butene (c2B) with TiCl3-(C2H5)3Al catalyst were studied. St and c2B were found to undergo a new type of monomer-isomerization copolymerization, i.e., only isomerization of 2B to 1-butene ( 1B ) took place to give a copolymer consisting of St and 1B units. The apparent copolymerization parameters were determined to be rst = 16.0 and rc2b = 0.003. The parameters were changed by the addition of NiCl2 (rSt = 8.4, rc2b = 0.05). The copolymers containing the major amount of St units were produced easily through monomer-isomerization copolymerization of St and 2B. © 1995 John Wiley & Sons, Inc. 相似文献
11.
Andrew K. Yaluma Peter J. T. Tait John C. Chadwick 《Journal of polymer science. Part A, Polymer chemistry》2006,44(5):1635-1647
Active center determinations on different Ziegler–Natta polypropylene catalysts, comprising MgCl2, TiCl4, and either a diether or a phthalate ester as internal donor, have been carried out by quenching propylene polymerization with tritiated ethanol, followed by radiochemical analysis of the resulting polymers. The purpose of this study was to determine the factors contributing to the high activities of the catalyst system MgCl2/TiCl4/diether—AlEt3. Active center contents (C*) in the range 2–8% (of total Ti present) were measured and a strong correlation between catalyst activity and active center content was found, indicating that the high activity of the diether‐containing catalysts is due to an increased proportion of active centers rather than to a difference in propagation rate coefficients. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1635–1647, 2006 相似文献
12.
Propylene polymerization reactions with supported Ziegler–Natta catalysts: Observing polymer material produced by a single active center
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Yury V. Kissin Vladimir P. Marin Patricia J. Nelson 《Journal of polymer science. Part A, Polymer chemistry》2017,55(23):3832-3841
Medium‐ and high‐resolution SEM analysis of several Ti‐based MgCl2‐supported Ziegler–Natta catalysts and isotactic polypropylene produced with them is carried out. Each catalyst particle, 35–55 μ in size, produces one polymer particle with an average size of 1.5–2 mm, which replicates the shape of the catalyst particle. Polymer particles contain two distinct morphological features. The larger of them are globules with Dav ~400 nm; from 1 to 2 × 1011 globules per particle. Each globule represents the combined polymer output of a single active center. The globules consist of ~2500 microglobules with an average size of ~20 nm. The microglobules contain several folded polymer molecules; they are the smallest thermodynamically stable macromolecular ensembles in propylene polymerization reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 3832–3841 相似文献
13.
Preparation of Polyethylene/Graphene Nanocomposites with Octadecylamine‐Modified Graphene Oxide‐MgCl‐Supported Ziegler–Natta Catalyst
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He‐Xin Zhang Jae‐Hyeong Park Young‐Kwon Moon Ko Eun‐Bin Xue‐Quan Zhang Keun‐Byoung Yoon 《Journal of polymer science. Part A, Polymer chemistry》2017,55(5):855-860
In this work, an octadecylamine‐modified graphene oxide (ODA‐GO)‐MgCl‐supported Ziegler–Natta catalyst was synthesized by reacting ODA‐GO with a Grignard reagent, followed by anchoring TiCl4 to the structure. The effect of the ODA‐GO on the catalyst morphology and ethylene polymerization behavior was examined. The resultant polyethylene (PE)/ODA‐GO nanocomposites directly mirrored the catalyst morphology by forming a layered morphology, and the ODA‐GO fillers were well dispersed in the PE matrix and showed strong interfacial adhesion with it. The resultant PE/ODA‐GO nanocomposites exhibited better thermal stability and mechanical properties than neat PE, even with a small amount of ODA‐GO added. Thus, this work provides a facile approach to the production of high‐performance PE. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 855–860 相似文献
14.
The very early stages of gas‐phase ethylene polymerization on an SiO2‐supported Ziegler–Natta catalyst were studied with the help of a short‐stop reactor. The short‐stop‐reactor‐based technique was useful in studying nascent polymerization, providing insights at very short, controlled times into important phenomena regarding catalyst fragmentation and the activation and deactivation of catalyst sites that take place during the very early stages of the reaction. Experimental results indicate that the growth of the polymer chains occurs at unsteady conditions during the initial stages of the polymerization. Hydrogen has a strong influence on the initial kinetics, leading to a significant decrease of polymerization activity. Polymer crystallinity increases with the reaction time, probably due to the formation of long chains with a high degree of crystallinity.
15.
L. Sun C. C. Hsu D. W. Bacon 《Journal of polymer science. Part A, Polymer chemistry》1994,32(11):2135-2145
A novel polymer-supported titanium-based catalyst shows high activity and nondecaying kinetic profiles for ethylene polymerization. The presence of 1-hexene comonomer drastically increases the catalyst activity, exhibiting a similarity to the MgCl2-supported catalysts. However, the nondecaying kinetic profiles of copolymerization distinguish this catalyst from the latter. Infrared analysis indicates that the transition metals were immobilized on the polymer support via functional groups. The effects of polymerization conditions on catalyst activity have been assessed. Characterization of the resulting polymer product by means of 13C-NMR, DSC, and SEM demonstrates a branch-free structure with high melting point, high crystallinity, and high molecular weight for the ethylene homopolymer. The reactivity ratios of ethylene-1-hexene copolymerization are evaluated from 13C-NMR analysis data. © 1994 John Wiley & Sons, Inc. 相似文献
16.
The magnesium chloride supported Ziegler–Natta catalysts are able to copolymerize ethylene and styrene in conditions of high activity. Different parameters, including catalyst type, monomer ratio, temperature and Lewis bases, allow variation of the activity and reactivity ratio. The incorporation of styrene in the copolymer remains always rather limited in moles. The products obtained contain less than 20% styrene in weight, and seem very similar in structure to linear low-density polyethylenes (LLDPE) obtained with the same catalyst: the melting temperature is only about 5°C lower than that of pure polyethylene. The polymer can be fractionated by solvents in a similar manner to LLDPE, and contains a styrene-enriched fraction, but homopolystyrene production has never been observed. 相似文献
17.
We present ab initio calculations on the Ziegler–Natta catalysis in heterogeneous conditions. Both cluster and periodic models with different basis sets have been used to explain the chemical reactivity of the various species that are involved. In heterogeneous conditions, several parameters contribute to the catalysis: the oxidation state of the titanium atom, the structure of the titanium site, the interaction with the support, MgCl2, and the cocatalyst, AlR3. This article yields to a synthetic view of the catalytic activity. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002 相似文献
18.
Preparation of polyethylene/lignin nanocomposites from hollow spherical lignin‐supported vanadium‐based Ziegler–Natta catalyst
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Shuwei Wang Na Feng Jiulai Zheng Keun‐Byoung Yoon Dongho Lee Minjie Qu Xuequan Zhang Hexin Zhang 《先进技术聚合物》2016,27(10):1351-1354
In the present article, a novel hollow spherical lignin‐supported vanadium‐based Ziegler–Natta catalyst was synthesized. The active centers of the obtained catalyst well dispersed in the lignin through the SEM‐EDX analysis. The resultant catalyst was investigated in ethylene polymerization and found to exhibit remarkable catalytic activity upon activation with ethylaluminium sesquichloride cocatalyst and ethyl trichloroacetate activator. During the polymerization, the lignin was gradually exfoliated by the polymerization force arising from the propagation of ethylene chain. The resultant PE/lignin nanocomposites preformed higher thermal stability compared to virgin PE. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
19.
H. L. Lu S. Hong T. C. Chung 《Journal of polymer science. Part A, Polymer chemistry》1999,37(15):2795-2802
This paper discusses the copolymerization reaction of propylene and p-methylstyrene (p-MS) via four of the best-known isospecific catalysts, including two homogeneous metallocene catalysts, namely, {SiMe2[2-Me-4-Ph(Ind)]2}ZrCl2 and Et(Ind)2ZrCl2, and two heterogeneous Ziegler–Natta catalysts, namely, MgCl2/TiCl4/electron donor (ED)/AlEt3 and TiCl3. AA/Et2AlCl. By comparing the experimental results, metallocene catalysts show no advantage over Ziegler–Natta catalysts. The combination of steric jamming during the consective insertion of 2,1-inserted p-MS and 1,2-inserted propylene (k21 reaction) and the lack of p-MS homopolymerization (k22 reaction) in the metallocene coordination mechanism drastically reduces catalyst activity and polymer molecular weight. On the other hand, the Ziegler–Natta heterogeneous catalyst proceeding with 1,2-specific insertion manner for both monomers shows no retardation because of the p-MS comonomer. Specifically, the supported MgCl2/TiCl4/ED/AlEt3 catalyst, which contains an internal ED, produces copolymers with high molecular weight, high melting point, and no p-MS homopolymer. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2795–2802, 1999 相似文献
20.
Yury V. Kissin 《Macromolecular theory and simulations》2002,11(1):67-76
The previously developed kinetic scheme for olefin polymerization reactions with heterogeneous Ziegler–Natta catalysts states that the catalysts have several types of active centers which have different activities, different stabilities, produce different types of polymer materials, and respond differently to reaction conditions. In the case of ethylene polymerization reactions, each type of center exhibits an unusual chemical feature: a growing polymer chain containing one ethylene unit, Ti—C2H5, is unusually stable and can decompose with the formation of the Ti—H bond. This paper examines quantitative kinetic ramifications of this chemical mechanism. Modeling of the complex kinetics scheme described in the Scheme demonstrates that it correctly and quantitatively predicts three most significant peculiarities of ethylene polymerization reactions, the high reaction order with respect to the ethylene concentration, reversible poisoning with hydrogen, and activation in the presence of α‐olefins. 相似文献