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Reported here in, is the synthesis of polystyrene (PS)-supported Ziegler–Natta catalyst (PS-TiCl4) by the reaction of PS and titanium tetrachloride (TiCl4). PS was synthesized by emulsion polymerization using super critical CO2 (sc-CO2) as a medium. Three catalysts were synthesized by varying the TiCl4/PS weight ratio in hexane medium. The resulting catalysts were characterized by Fourier transformed-infrared spectroscopy, UV–visible spectroscopy, scanning electron microscope and energy dispersive X-ray detector, X-ray diffraction analysis. The acidity of the catalysts in an acetone/water solution was measured by pH meter. The thermogravimetric analysis reveals that catalysts are stable upto 150–180°C. Due to their higher degree of thermal stability these catalysts may potentially be used as a support in conventional Ziegler–Natta catalyst for ethylene polymerization. These catalysts also showed good storability and its overall catalytic productivity are found to be 3720 g PE/g Ti. The productivity of the catalysts also depended on the titanium concentration in the polymer matrix. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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Paula Zapata Raúl Quijada Cristian Covarrubias Edwin Moncada Jaime Retuert 《应用聚合物科学杂志》2009,113(4):2368-2377
Catalytic activity during the formation of polyethylene (PE)/clay nanocomposites by in situ polymerization with metallocenes was studied. Ethylene polymerization was carried out with the homogeneous metallocene in the presence of the clay particles and using the clay‐supported metallocene catalyst. It was found that the catalytic activity of the homogeneous metallocene does not decrease in the presence of the clay particles and only a slight decrease of activity occurs using the clay‐supported catalyst. The modification of the clay with MAO cocatalyst as well as its intercalation with ODA surfactant were found to play an important role during the in situ formation of the PE/clay nanocomposite. ODA‐intercalated clay apparently facilitates the activation and monomer insertion processes on zirconocene centers located in internal sites of the clay structure. Although metallocene supported on MAO‐treated clay exhibited somewhat lower catalytic activity than that supported directly on the ODA‐intercalated clay, both systems favored the production of PE nanocomposites containing highly exfoliated clay particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009 相似文献
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非均相有机铬系催化剂是工业上常用的聚乙烯催化剂,20世纪60年代被广泛应用于气相法高密度聚乙烯的生产。生产的高密度聚乙烯产品分子量分布宽,长支链含量高,在加工生产高强膜和耐压聚乙烯管材等高附加值产品时具有独特的优势,近年来成为研究热点。按其负载后活性组分的不同,有机铬系催化剂可分为二茂铬和铬酸酯类。综述有机铬系催化剂的发展历程、催化剂及其前驱体的制备和催化剂结构及聚合产品特性,指出可应用于冷凝态操作的高效高活性有机铬系催化剂是今后的研发方向。由于非均相铬系催化剂结构和反应机理复杂,研究其微观机理仍面临很多瓶颈。 相似文献
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Polyethylene was prepared by using a nBu-Cp2ZrCl2/MAO catalytic system. Considering the reactivation of Zr species, a novel and reasonable mathematical model of kinetics has been developed and the kinetic profiles of ethylene polymerization have been fitted satisfactorily. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 3186–3189, 2001 相似文献
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A mathematical model, including the main morphological features of the polymerization process, is developed to study olefin polymerization with supported metallocene catalysts. Because the relatively large amount of methyl alumoxane (MAO) usually needed as a cocatalyst represents a disadvantage, the model introduces a scheme that simulates the results of the efforts being made in a supported catalyst to reduce MAO requirements to commercially acceptable levels. Critical fragmentation steps in the initial support‐catalyst particles that render all active sites effectively available to the monomer are specifically considered, on the basis of the support morphological characteristics. With the available reaction data, fragmentation representation alternatives are discussed and a scheme proposed. Then, a mathematical model is developed based on the above representation scheme, to calculate monomer‐concentration, temperature, and macroparticle‐size evolutions. The main features of the scheme are displayed and discussed. Both for laboratory and high‐productivity conditions, the model is used to predict changes in macro‐ and microparticle size, porosity, and concentration distribution. Predictions are employed to evaluate the impact of the initial support microparticle arrangement and fragmentation processes on the overall catalyst performance. Polymer yield, concentration profiles, and temperature transients predicted by the model are presented, showing the model application after verifying its accordance with the available experimental data. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 285–311, 2001 相似文献
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Chiu-Hsun Lin 《Catalysis Letters》2000,68(1-2):63-65
By utilizing a pre-mixing method, we can prepare a supported metallocene catalyst producing a polyethylene of larger granular
size and containing fewer fine particles than that prepared by the conventional adsorption of metallocene on a MAO-coated
SiOx surface. Such supported catalyst helps to eliminate the reactor fouling during polymerization of ethylene.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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两性离子催化剂按照配体的结构特征和金属元素种类可分为两性离子茂金属配合物、非茂前过渡以及后过渡金属两性离子配合物三大类。两性离子茂金属配合物根据阴离子在配体上所连接区域的不同又可以分为Girdle型、Bridge型和Ring型三种。本文对各类两性离子配合物的合成方法、结构特征和催化反应活性进行了归纳总结,发现两性离子催化剂对催化烯烃聚合表现出较好的活性,而非茂的两性离子配合物不仅是良好的烯烃聚合催化剂,还可以催化多种类型的小分子反应。作为一种新型高效的单组份活性催化剂,目前,有关两性离子催化剂的应用研究还有很多未知的领域有待开发,尤其是在小分子的活化、催化领域。 相似文献
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研究金属茂均相催化剂中过渡金属的性质对乙烯聚合的影响。以丁烯基取代的二茂二氯化锆(CpBu)2ZrCl2和丁烯基取代的二茂二氯化锆(CpBu)2HfCl2与甲基铝氧烷组成的均相催化剂体系,对乙烯聚合进行了较详细的比较研究。 相似文献
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Naeimeh Bahri‐Laleh Hassan Arabi Shahram Mehdipor‐Ataei Mehdi Nekoomanesh‐Haghighi Gholamhosein Zohuri Mehrdad Seifali Zahra Akbari 《应用聚合物科学杂志》2012,123(4):2526-2533
Several organohalide (HC) compounds were tested as promoters for a Ti‐based Ziegler‐Natta (Z‐N) catalyst at different polymerization conditions. Results show that the intensity of the promoting effect depends on the nature and amount of the promoters. A proper amount, especially optimum amount, of aliphatic type organohalides leads to a strong productivity, and aromatic ones leads to a weak productivity improvement; however, 3‐chloro‐1‐propene poison the catalyst even at lower HC/Ti molar ratios. Among studied compounds, chlorocyclohexane has the best activity promotion effect at HC/Ti molar ratio of 128, and with this as a promoter, the activity increases over 85%. To understand more details about this phenomenon, the rate of polymerization during time and the effect of polymerization conditions (the temperature and hydrogen partial pressure) on the performance of chlorocyclohexane as the most effective promoter were studied. Finally, to explore the mechanism of reactivation of catalyst species by organohalides, molecular modeling was employed and a new oxidation‐addition mechanism was proposed, which basically consisting of homolytic breaking of C? Cl bond in organohalides. It was found that reoxidation of the catalyst, restoring active center, by Cl rich organohalides is energetically more favored. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
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For ethylene polymerization, the supported metallocene catalyst was prepared by anchoring CpIndZrCl2 on silica with an appropriate spacer. The three procedures were applied for CpIndZrCl2 anchoring on silica with a hexamethyltrisiloxane or pentamethylene spacer. The anchoring procedures exerted a strong influence on the catalyst activity since the different anchoring methods gave the formation of different structures of active sites. With the new anchoring route, it was possible to prepare the “heterogeneous single‐site” catalyst which was found to have only one catalyst structure on silica and exhibited a higher catalyst activity than that of the other supported catalysts. At a polymerization temperature of 70°C, the activity of the heterogeneous single‐site catalyst was comparable to that of the unsupported homogeneous zirconocene. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 1071–1080, 1999 相似文献
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A. J. D. de Freitas J. H. Z. dos Santos S. M. P. Meneghetti M. R. Meneghetti 《应用聚合物科学杂志》2011,119(5):3051-3057
The development of metallocene‐based catalysts is an important advance on the study of polyolefinic materials. However, due to the rather different conditions that are established in actual applications, only around 3% of these polymers are obtained from metallocene technology. In view of this, novel strategies must be developed to produce metallocene‐based catalysts that are more thermally stable, which is a fundamental requirement to establish metallocene technologies. Homogeneous and heterogeneous polymerizations of ethylene were compared, using the Ph2C(Cp)(Flu)ZrCl2/MAO system. Homogeneous polymerizations were more active than the corresponding supported reactions. At low ethylene pressure, the addition of 1‐hexene increases the activity under homogeneous conditions. Nevertheless, this is not observed on the respective supported systems. At higher pressure conditions, all polymerizations attained higher yields. However, when the reaction temperature increases the activity significantly decreases under homogeneous conditions. Furthermore, when the polymerization was performed under heterogeneous conditions the deactivation was lower. The homogeneous and supported catalytic systems show different characteristics and, in all attempted reactions, immobilization of the molecular catalyst reduces the activity. However, the deactivation ratio was lower when the polymerization was performed under heterogeneous conditions. This means that immobilization of Ph2C(Cp)(Flu)ZrCl2 on silica can improve the thermal stability of the catalytic species. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010 相似文献
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介绍了含氧,氮等杂原子单活性中心催化剂,包括后过渡金属催化剂,应用于乙烯,α-烯烃,环烯烃及其他极性单体的聚合。 相似文献
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An asymmetric 3‐oxa‐pentamethylene bridged dinuclear titanocenium complex (CpTiCl2)2(η5‐η5‐C9H6(CH2CH2OCH2CH2)C5H4) ( 1 ) has been prepared by treating two equivalents of CpTiCl3 with the corresponding dilithium salts of the ligand C9H7(CH2CH2OCH2 CH2)C5H5. The complex 1 was characterized by 1H‐, 13C‐NMR, and elemental analysis. Homogenous ethylene polymerization catalyzed using complex 1 has been conducted in the presence of methylaluminoxane (MAO). The influences ofreaction parameters, such as [MAO]/[Cat] molar ratio, catalyst concentration, ethylene pressure, temperature, and time have been studied in detail. The results show that the catalytic activity and the molecular weight (MW) of polyethylene produced by 1 /MAO decrease gradually with increasing the catalyst concentration or polymerization temperature. The most important feature of this catalytic system is the molecular weight distribution (MWD) of polyethylene reaching 12.4, which is higher than using common mononuclear metallocenes, as well as asymmetric dinuclear titanocene complexes like [(CpTiCl2)2(η5‐η5‐C9H6(CH2)nC5H4)] (n = 3, MWD = 7.31; n = 4, MWD = 6.91). The melting point of polyethylene is higher than 135°C, indicating highly linear and highly crystalline polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
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Maria De Fátima Vieira Marques Anunciata Conte Flávia C. De Resende Érica Gervasoni Chaves 《应用聚合物科学杂志》2001,82(3):724-730
In this work, the performance of the homogeneous catalyst system based on Et(Flu)2ZrCl2/MAO was evaluated on the copolymerization of ethylene and 1-octene. Characteristics of some of the produced polymers were also investigated. A study was performed to compare this system with that of Cp2ZrCl2/MAO. The influence of different support materials for the Cp2ZrCl2 was also evaluated, using silica, MgCl2, and the zeolite sodic mordenite NaM. An increase in activity was observed in relation to the comonomer addition for the two homogeneous catalysts. The copolymers produced by the Et(Flu)2ZrCl2/MAO system showed higher molecular weight and narrower molecular weight distribution. We verified that the catalyst supported on SiO2 was the most active one, although the copolymers produced with the catalyst supported on NaM showed higher molecular weight and lower molecular weight distribution. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 724–730, 2001 相似文献
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通过引入卤代醇类化合物制备了适用于乙烯淤浆聚合工艺的新型高性能Ziegler-Natta催化剂(简称GH催化剂)。采用分光光度计、扫描电子显微镜等表征了催化剂的组成、粒径和形态等;采用淤浆聚合法研究了催化剂的聚合性能,并与国产商业化催化剂(参比催化剂)进行了比较。结果表明:GH催化剂的活性达21.6 kg/g,聚乙烯堆密度达0.34 g/cm3,粒径≥75~830μm的聚乙烯粉料质量占聚乙烯粉料总质量的97.9%,且GH催化剂的氢调敏感性和其催化乙烯与1-己烯共聚合的性能均优于参比催化剂。 相似文献
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μ‐Gels which consist of poly(organosilicon) networks can be employed as efficient support materials for ethylene polymerization catalyst precursors. Alkylaluminum cocatalysts can be fixed on the μ‐gel surfaces using the PHT (“partially hydrolyzed trimethylaluminum”) method. The influence of different aluminum/water ratios on the ethylene polymerization properties of these heterogeneous systems is investigated. Dinuclear silicon bridged zirconium complexes are used as catalyst precursors yielding polyethylenes with broad or bimodal molecular weight distributions. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献