共查询到20条相似文献,搜索用时 0 毫秒
1.
T. E. Nowlin R. I. Mink F. Y. Lo T. Kumar 《Journal of polymer science. Part A, Polymer chemistry》1991,29(8):1167-1173
The amount of dibutylmagnesium (DBM) or triethylaluminum (TEAL) that reacted with silica at 55–60°C depended on the silica calcining temperature. Lower silica calcining temperatures resulted in more Mg or Al fixed to the silica surface, indicating greater amounts of DBM or TEAL reacting with the silica. The amount of the metal alkyls butyl(octyl) magnesium ethoxide, ethylaluminum dichloride, tri-n-hexylaluminum, and diethyl(ethyldimethylsilanolato) aluminum that reacted with 600°C calcined silica was also determined. The metal alkyl can react with the silica at two sites, a surface hydroxyl group and a siloxane group. The silica surface hydroxyl groups can be chemically converted to trimethylsilyl groups so that only the siloxane groups are available for attack. After the metal alkyl was reacted with silica, the resulting intermediate was treated with titanium tetrachloride to yield an ethylene polymerization catalyst in the presence of TEAL. When no metal alkyl was employed, titanium tetrachloride reacted only with the silica surface hydroxyl groups to yield a weakly active ethylene polymerization catalyst. 相似文献
2.
Ruicheng Ran 《Journal of polymer science. Part A, Polymer chemistry》1993,31(6):1561-1569
A polymer-supported Ziegler–Natta catalyst, polystyrene-TiCl4AlEt2Cl (PS–TiCl4AlEt2Cl), was synthesized by reaction of polystyrene–TiCl4 complex (PS–TiCl4) with AlEt2Cl. This catalyst showed the same, or lightly greater catalytic activity to the unsupported Ziegler–Natta catalyst for polymerization of isoprene. It also has much greater storability, and can be reused and regenerated. Its overall catalytic yield for isoprene polymerization is ca. 20 kg polyisoprene/gTi. The polymerization rate depends on catalyst titanium concentration, mole ratio of Al/Ti, monomer concentration, and temperature. The kinetic equation of this polymerization is: Rp = k[M]0.30[Ti]0.41[Al]1.28, and the apparent activation energy ΔEact = 14.5 kJ/Mol, and the frequency factor Ap = 33 L/(mol s). The mechanism of the isoprene polymerization catalyzed by the polymer-supported catalyst is also described. © 1993 John Wiley & Sons, Inc. 相似文献
3.
Maria M. V. Marques Clemente Pedro Nunes Peter J. T. Tait Alberto Romo Dias 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):219-225
This article describes studies on the variables that regulate the molecular weight in ethylene polymerization using a highly active Ziegler–Natta catalyst with hydrogen for molecular weight control. The dependence of the degree of polymerization on the concentration of catalyst, cocatalyst, monomer, partial pressure of hydrogen, and temperature has been established. The rate constant for chain transfer with cocatalyst has been evaluated. © 1993 John Wiley & Sons, Inc. 相似文献
4.
Enzo Giannetti Giuseppe Martino Nicoletti Romano Mazzocchi 《Journal of polymer science. Part A, Polymer chemistry》1985,23(8):2117-2134
Homogeneous Ziegler-Natta systems for the ethylene polymerization, deriving from R2R2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ-alkyl and the π-cyclo-pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ-alkyl derivatives of IVB transition metals, such as Zr(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity. Active species containing Zr? O? Al bonds have been postulated. 相似文献
5.
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
6.
Maria M. V. Marques Clemente Pedro Nunes Peter J. T. Tait Alberto Romo Dias 《Journal of polymer science. Part A, Polymer chemistry》1993,31(1):209-218
Factors affecting the particular shape of kinetic rate–time profiles in the polymerization of ethylene with a MgCl2-supported TiCl4 catalyst activated by Al(C2H5)3 have been investigated. Examination of the dependence of the polymerization rate on the concentration of Al(C2H5)3 resulted in a Langmuir–Hinshelwood rate law. Analysis of the polymerization rate as a function of the polymerization temperature gave about 46 kJ mol?1 for the overall activation energy. Examination of the rapid decay of the polymerization rate with time showed that this decay is represented better by a first-order decay law than by a second-order one. © 1993 John Wiley & Sons, Inc. 相似文献
7.
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
8.
Motonobu Furuta 《Journal of Polymer Science.Polymer Physics》1981,19(1):135-141
The surface composition of TiCl3-based Ziegler—Natta catalysts prepared by various methods was analyzed by ESCA to correlate the total amount of surface titanium with the catalyst activity in propylene polymerization. The ESCA peak ratio (Ti 2P3/2/Cl 2P) of the catalysts was measured to estimate the surface composition. The titanium index defined as the product of the (Ti/Cl peak ratio and surface area) was closely correlated with the catalyst activity in polymerization. This indicates that surface titanium concentration and surface area determine the catalyst activity. It was also found that removal of surface aluminum and chlorine at the catalyst preparation stage results in concentration of titanium at the surface and an increase in surface area. 相似文献
9.
Zhao‐Yang Ye Li Wang Lian‐Fang Feng Xue‐Ping Gu Hai‐Hua Chen Pu‐Yu Zhang Jie Pan Shan Jiang Lin‐Xian Feng 《Journal of polymer science. Part A, Polymer chemistry》2002,40(18):3112-3119
Spherical MgCl2 adducts used as supports for a Ziegler–Natta catalyst for olefin polymerization were prepared by the general precipitation method. The influence of MgCl2/EtOH (mol/mol) and the dispersion speeds on the particle size (PS) and particle size distribution (PSD) were investigated. It was found that the former played a trivial role in controlling the PS and PSD, and the latter was the key factor. In particular, the influence of ethanol on the crystal structure was further examined, with consideration given to the performance of the supported Ziegler–Natta catalyst. It was believed that the reactions between MgCl2 and ethanol had a controlling effect on the destruction of the original anhydrous MgCl2, which was the key point in the preparation of suitable supports for the latest generation Ziegler–Natta catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3112–3119, 2002 相似文献
10.
David L. Beach Yury V. Kissin 《Journal of polymer science. Part A, Polymer chemistry》1984,22(11):3027-3042
Synthesis of low-density polyethylene, that is, a density of less than 0.925 g/cm3, has traditionally been accomplished by the use of free-radical initiators at high ethylene pressures or of an alpha olefin comonomer such as 1-butene at lower pressures. We investigated an alternative route to branched, low-density polyethylene with a single monomer, ethylene, as the feed in conjunction with multicomponent catalyst systems capable of in situ dimerization of ethylene and subsequent copolymerization to produce low-density polyethylene. This article discusses the details of the evaluation of a number of dual-functional systems based on Ziegler-Natta catalysts. Specific, well defined, dual-functional catalyst systems which could easily produce branched, low-density polyethylene with levels of 20–30 branches per 1000 carbon atoms were developed. Variations in the relative number of component catalysts resulted in systematic, predictable changes in the properties of the polyethylene produced, which demonstrated the utility of the dual-functional catalyst concept. 相似文献
11.
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
12.
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
13.
Kiyoshi Endo Hiroharu Nagahama Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1979,17(11):3647-3653
A study of the monomer isomerization polymerization of 2-, 3-, and 4-octenes has been made with TiCl3–(C2H5)3Al catalyst at 80°C in comparison with the ordinary polymerization of 1-octene. It was found that all these octenes underwent monomer-isomerization polymerization to give high-molecular-weight homopolymer consisting exclusively of the 1-octene unit. The addition of an isomerization catalyst such as nickel acetylacetonate accelerated this polymerization. The rates of polymerization were found to decrease in the following order: 1-octene > 2-octene > 3-octene > 4-octene. These results indicate that the isomerization proceeded by a stepwise double-bond migration. It was also found that the monomer-isomerization copolymerization of 2-octene and 2-butene occurred under similar conditions and produced copolymers of both 1-olefin units. 相似文献
14.
15.
T. E. Nowlin Y. V. Kissin K. P. Wagner 《Journal of polymer science. Part A, Polymer chemistry》1988,26(3):755-764
High activity ethylene polymerization catalysts have been prepared by the interaction of ethylmagnesium chloride in tetrahydrofuran with high surface area silica, followed by reaction with excess titanium tetrachloride in heptane. The catalysts were tested in ethylene—hexene copolymerization reactions in the presence of AlEt3 at 80°C. For comparison purposes, the copolymerization properties of a similar catalyst prepared without silica were also evaluated. Preparative conditions were identified which provide catalysts that possess high reactivity towards 1-hexane. The silica and the amount of magnesium used in catalyst preparation strongly affect the copolymerization properties of the catalysts. Generally, catalysts prepared with silica showed much higher sensitivity to 1-hexene (effective reactivity ratio r1 = 25–60) while a similar catalyst prepared without silica exhibited an r1 value of 125. Fractionation of the copolymer with a series of boiling solvents showed that all the catalysts exhibit a wide distribution of active centers with respect to reactivity ratios, with the r1 values varying from 5–7 to ca. 200. The width of a the center distribution depends on catalyst composition—it is the narrowest for the catalyst prepared without silica and is the widest for the catalysts with intermediate Ti : Mg ratios. 相似文献
16.
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
17.
J. Jarrin F. Dawans E. Marechal S. Boileau 《Journal of polymer science. Part A, Polymer chemistry》1984,22(10):2345-2352
Some new TiCl4/Crown ether complexes were synthesized and used as polymerization catalysts with AlEt3 or AlEt2Cl as cocatalyst for the stereospecific polymerization of 1,3-butadiene. As with most of the nucleophilic ligands the addition of crown ethers to Ziegler–Natta catalytic systems results in a decrease of the polymer conversion. But the Al/Ti molar ratio appears to be less critical for the complexed systems than for the uncomplexed ones. The presence of the crown ether in the surroundings of the catalytic sites presumably protects them from an excess of the organoaluminum cocatalyst. The side groups of the crown ether do not influence the microstructure of the polybutadiene obtained but they change the activity of the catalytic systems. Thus, the electron-donating effect of the macrocyclic ligands seems to be less important than the sterical effect due to the rigidity and to the hole size of the crown ether. 相似文献
18.
Kiyoshi Endo Takayuki Otsu 《Journal of polymer science. Part A, Polymer chemistry》1991,29(5):643-649
Monomer-isomerization polymerization of propenycyclohexane (PCH) with TiCl3 and R3-xAICIx (R = C2H5 or i-C4H9, x = 1–3) catalysts was studied. It was found that PCH underwent monomer-isomerization polymerization to give a high molecular weight polymer consisting of an allylcyclohexane (ACH) repeat unit. Among the alkyaluminum cocatalysts examined, (C2H5)3Al was the most effective cocatalyst for the monomer-isomerization polymerization of PCH, and a maximum for the polymerization was observed at a molar ratio of Al/Ti of about 2.0. The addition of isomerization catalysts such as nickel acetylacetonate [Ni(acac)2] to the TiCl3–(C2H5)3Al catalyst accelerated the monomer-isomerization polymerization of PCH and gave a maximum for the polymerization at a Ni/Ti molar ratio of 0.5. PCH also undergoes monomer-isomerization copolymerization with 2-butene (2B). 相似文献
19.
Alain Siove Michel Fontanille 《Journal of polymer science. Part A, Polymer chemistry》1984,22(12):3877-3884
Polymerization of ethylene was initiated with soluble polystyrene100-butadiene3-Li/TiCI4 complexes in toluene leading to block copolymers. The activity of the system was measured at a constant ratio r = [Li]/[Ti] and for different concentrations in active centers and in monomer. Measurement of the amount of the block copolymers formed led to the direct determination of the efficiency of the catalytic system. This efficiency is defined with respect to the number of potentially active centers and is close to 90%. From both measured values of activity of the catalytic system and of its efficiency, the rate constants of propagation were deduced. The kinetic behavior of the system is fully consistent with that of a living system. The rate is first order towards both ethylene and active centers concentrations. So, the rate constant of propagation is an absolute rate constant, measuring the intrinsic reactivity of active sites. Determination of the absolute rate constant at different temperatures, led to thermodynamic parameters of the propagation reaction. The chemical composition of the complex and the absence of polymeric aggregation, leads to propose a structure of the active species: a bioctahedral binuclear structure is consistent with kinetic, thermodynamic results, and structural determinations. 相似文献
20.
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