Observation of bimodal polyethylene derived from TiO2-supported zirconocene/MAO catalyst during polymerization of ethylene and ethylene/1-hexene

The bimodal polyethylene obtained from TiO₂-supported zirconocene/MAO catalyst was observed during polymerization of ethylene and ethylene/1-hexene. By means of XPS, it revealed that TiO₂ consisted of Ti³⁺ (BE = 462.6 eV) and Ti⁴⁺ (BE = 464.9 eV). The dual catalytic sites were attributed to the presence of Ti³⁺ and Ti⁴⁺ in TiO₂.     

Supported zirconocene catalyst for preventing reactor fouling in ethylene polymerization

The commercial interest of metallocene complexes for olefin polymerization has led to additional efforts to prepare suitable metallocene complexes efficiently and economically. Ethylene polymerization was carried out with a series of heterogeneous catalysts which were prepared in various Zr/silica ratios by immobilization of Ind₂ZrCl₂ preactivated with methylaluminoxane (MAO) on silica. This method to form the catalyst system resulted in a polymerization catalyst with reduced fouling tendencies and improved reactor operability. Polymerization of ethylene was conducted in Buchi reactors in a slurry phase under mild pressure. Some of the physical properties of the obtained polymers were also determined. Copyright © 2005 Society of Chemical Industry     

负载茂金属催化剂催化乙烯气相聚合

研究了负载茂金属催化剂(n-BuNeCp)_2ZrCl_2/SiO_2的乙烯气相聚合行为及其催化聚合产品的性能。三乙基铝加入聚合体系后可降低负载茂金属催化剂的初始活性,有利于聚合过程中的温度控制。气相聚合产品聚乙烯的重均分子量为(1 42～2.28)×10~5,相对分子质量分布为2.6～3.1,熔点在135℃以上,结晶度约为60%,聚乙烯产物颗粒形态以球形为主.堆密度大于0.35 g/cm~3。     

FTIR investigation of ethylene coordination and polymerization on reduced Cr/SiO2 catalyst

FTIR spectroscopy was applied to study the initial steps of ethylene polymerization on reduced chromia-silica (0.5 wt% Cr/SiO₂). To decrease the speed of the reaction small doses of gas were introduced to the catalyst in each run and C₂D₄ was used to confirm band assignments. At the initial steps of the reaction only ethylene molecules coordinated to probably Cr _A ²⁺ cations were observed. The concentration of such complexes was estimated to be about 50% of the total amount of Cr atoms in the sample. The FTIR spectrum of the polymer formed at the initial doses of C₂H₄ (when [C₂H₄] [Cr]) was found to be slightly different from that formed after excess ethylene was introduced onto the catalyst ([C₂H₄] > [Cr]).     

Effects of trisobutylaluminium on styrene polymerization with Ni(acac)2 /MAO/SiO2 catalyst system activated by methylaluminoxane

Summary Styrene polymerization with Ni(acac)₂/MAO/SiO₂ catalytic system was carried out in the presence of methylaluminoxane (MAO), triisobutylaluminum (TIBA) or MAO and TIBA mixture as activators. The catalytic system activated only by TIBA produced polymer with 53% of isotacticity. When the catalytic system was activated by a mixture of MAO and TIBA the polymer isotacticity increases as MAO concentration increases. In this case, the maximum of isotacticity was 59%. The polymer has presented lower molecular weight than the polymer obtained by MAO as activators and the polymer microstructure was not explained by Markov first-order model. In addition, ¹³C NMR spectra of the polymers obtained after extraction with MEK, have indicated that there are two active sites in this catalytic system. Received: 28 November 2001 / Revised version: 24 May 2002 / Accepted: 29 May 2002     

Nano‐sized silica supported Me2Si(Ind)2ZrCl2/MAO catalyst for ethylene polymerization

Nano‐sized and micro‐sized silica particles were used to support a zirconocene catalyst [racemic‐dimethylsilbis(1‐indenyl)zirconium dichloride], with methylaluminoxane as a cocatalyst. The resulting catalyst was used to catalyze the polymerization of ethylene in the temperature range of 40–70°C. Polyethylene samples produced were characterized with scanning electron microscopy (SEM), X‐ray diffraction (XRD), differential scanning calorimetry (DSC), and gel permeation chromatography (GPC). Nano‐sized catalyst exhibited better ethylene polymerization activity than micro‐sized catalyst. At the optimum temperature of 60°C, nano‐sized catalyst's activity was two times the micro‐sized catalyst's activity. Polymers obtained with nano‐sized catalyst had higher molecular weight (based on GPC measurements) and higher crystallinity (based on XRD and DSC measurements) than those obtained with micro‐sized catalyst. The better performances of nano‐sized catalyst were attributed to its large external surface area and its absence of internal diffusion resistance. SEM indicated that polymer morphology contained discrete tiny particles with thin long fiberous interlamellar links. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Supported SiO2‐nBuSnCl3/MAO/(nBuCp)2ZrCl2 catalyzing MAO cocatalyst‐free ethylene polymerization: Study of hydrogen responsiveness

A supported metallocene catalyst was synthesized by sequentially loading methylaluminoxane (MAO) (30 wt % in toluene) and (ⁿBuCp)₂ZrCl₂ on partially dehydroxylated silica ES 70 modified by ⁿBuSnCl₃. Its shock load hydrogen responsiveness was evaluated by polymerizing ethylene for 1 h at 8.5 bar (g) and 75°C without separately feeding the MAO cocatalyst. The shock load hydrogen feeding increased the ethylene consumption (at a fairly constant rate), catalyst productivity, as well as the resin bulk density and average particle size at ΔP (of hydrogen) ≥～3.0 psi. The bulk density increased from 0.25 to 0.31 g/cm³. This shows a procedure for overcoming the inherent drop in catalyst productivity caused by heterogenization of metallocenes (that is a method for catalyst activation) and improving the resulting resin bulk density. The volume‐weighted mean particle diameter of the resulting polyethylenes was found to be 5.80–11.12‐fold that of the catalyst corresponding to ΔP = 0.00–7.11 psi, respectively. The resulting kinetic profiles showed to be fairly stable. However, M_w and polydispersity index were not affected. The particle size distribution, average particle size, and the scanning electron microscope photographs of the resulting resin particles confirmed the occurrence of the replication phenomenon. On the basis of the above findings, the mechanism of ethylene polymerization under the present experimental conditions has been revisited. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Synthesis of polyethylene/coir dust hybrid filler via in situ polymerization with zirconocene/MAO catalyst for use in natural rubber biocomposites

In This study, polyethylene/coir dust hybrid filler was synthesized by in situ polymerization using a zirconocene/MAO catalytic system. The obtained hybrid filler was then used for the production of natural rubber biocomposites. The synthesis process of the filler was investigated with variation of coir dust loadings. It was found that increasing the amount of coir dust decreased the catalytic activities due to negative supporting effects. After introducing the PE/coir dust hybrid filler into natural rubber, SEM micrographs showed that the PE/coir dust filler were more compatible with the natural rubber matrix than the pure coir dust. This is owing to the hydrophobicity of the polyethylene in the hybrid filler. The results from a dynamic mechanical analysis showed that the natural rubber biocomposites with the hybrid filler provided a greater storage modulus than that with the pure coir dust. This suggests that the enhanced stiffness of the natural rubber biocomposites is probably due to the strong interaction between the hybrid filler and the natural rubber matrix. The strong interaction in the biocomposite can be confirmed by the low value of a loss factor (tan δ), which indicates a low degree of molecular mobility of the polymer chains, resulted from good adhesion on the filler surfaces.     

Study of ethylene polymerization catalyzed by nBu-Cp2ZrCl2/MAO catalytic system and their polymerization kinetics

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     

MgCl2-BuOH/TiCl4催化剂催化乙烯聚合动力学

研究了MgCl2-正丁醇/TiCl4催化剂常压下催化乙烯聚合的性能和动力学行为.考察了n(Al)/n(Ti)、聚合温度、共聚单体浓度、氢气分压对催化剂性能的影响.研究表明:三乙基铝为助催化剂,n(Al)/n(Ti)为200,聚合压力为0.1 MPa,温度为50℃,聚合时间为2 h时,该催化剂具有较高的活性:聚合动力学行为平稳,活性衰减较慢,活性可达1 550.2 g/g;该催化剂具有良好的乙烯均聚合和共聚合性能以及氢调性能.     

新型MgCl2/SiO2复合载体丙烯聚合催化剂的研究

采用喷雾干燥法制备了MgCl2/SiO2球形复合载体,经载钛处理后得到丙烯聚合催化剂。利用SEM、XRD、XPS、EDX等分析了催化剂的形态和物性,并进行了丙烯本体聚合研究。结果表明:负载TiCl4后制备出的球形丙烯聚合催化剂中,Ti/Mg活性组分均匀负载于SiO2堆成的微球中,催化剂保持了良好的颗粒形态。该催化剂用于丙烯聚合,具有催化活性高、立体定向性好、氢调敏感性好等特点。     

SiO2负载二亚胺镍/TiCl4催化乙烯聚合

合成了配合物N,N'-二[4-(4-氨基-3,5-二乙基苄基)-2,6-二乙基苯基]苊二亚胺二氯化镍(NiLCl2),将其与TiCl4复合负载在SiO2/MgCl2上制得负载催化剂.研究了该负载催化剂对乙烯聚合的催化活性, 考察了聚合条件对聚合反应及产物结构的影响.结果表明,负载的NiLCl2/TiCl4较之未负载的NiLCl2催化活性高,最高催化活性达到552 kg/(mol·h),而聚合需要的n(Al)/n(Ni)也较相应的NiLCl2低.     

Ethylene polymerization over a nano-sized silica supported Cp2ZrCl2/MAO catalyst

Nano-sized and micro-sized silica particles were used to support Cp₂ZrCl₂/MAO catalyst for ethylene polymerization. Nano-sized catalyst exhibited much better ethylene polymerization activity than micro-sized catalyst. At the optimum temperature of 60 °C, nano-sized catalyst’s activity was 4.35 times the micro-sized catalyst’s activity, which was attributed to the large specific external surface area, the absence of internal diffusion resistance, and the better active site dispersion for the nano-sized catalyst. Polymers produced were characterized with SEM, XRD, DSC, and densimeter. SEM indicated that the resulting polymer morphology contained discrete tiny particles and thin long fiberous interlamellar links.     

The influence of the preparing conditions of SiO2 supported Cp2ZrCl2 catalyst on ethylene polymerization

In this work, ethylene was polymerized by using Cp₂ZrCl₂ supported on silica pretreated with methylaluminoxane (MAO) as the catalyst system. The influence of the conditions for the preparation of the heterogeneous catalyst, such as temperature, washing method of the catalytic solid, MAO and metallocene concentration in the support treatment, time of MAO, and metallocene immobilization on the support, type of alkylaluminum used in the support pretreatment, and calcination temperature of the support were investigated. Aluminum and zirconium content fixed on the silica surface were determined by inductively coupled plasma emission spectroscopy. Polymer characteristics were determined by gel permeation chromatography and differential scanning calorimetry. According to the results, the activity of some supported catalysts were far higher than with the homogeneous system. Moreover, polyethylene with very high molecular weights were also obtained and with molecular weight distribution larger than those produced with the homogeneous precursor. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2054–2061, 2002     

Copolymerization of ethylene and 1-octadecene with the Cp2ZrCl2/MAO and Cp2HfCl2/MAO catalyst systems

Summary The comparison of the copolymers obtained with the Cp₂ZrCl₂/MAO and Cp₂HfCl₂/MAO catalyst systems showed that the catalyst having hafnocene was much more reactive towards 1-octadecene than zirconocene. The comonomer concentration had to be three times higher in the zirconocene copolymerization than in the hafnocene copolymerization when the level of 6 mol-% was reached. Although the hafnocene catalyst was more reactive towards 1-octadecene, the molecular weights were higher than in the copolymers obtained with the zirconocene catalyst.The total activity of the zirconocene was 10 times higher than with the hafnocene catalyst. With the zirconocene catalyst the activity towards ethylene was constantly increasing by increasing the comonomer concentration but stayed nearly constant with the hafnocene catalyst. It seemed that there is no rate enhancement effect upon comonomer addition with the hafnocene catalyst.     

新型菲咯啉基铁催化剂/MAO催化乙烯齐聚

合成了配合物氯化2-乙酰基-1,10-菲咯啉缩4-甲基-2,6-二乙基苯胺合铁(Ⅱ),以甲苯为溶剂,甲基铝氧烷(MAO)为助催化剂,催化乙烯齐聚制备线型α-烯烃。研究了反应温度、n(Al)/n(Fe)和反应压力等对催化剂活性和齐聚产物分布的影响,在n(Al)/n(Fe)为1 000,温度为60℃,压力4.0 MPa下,催化剂活性达1.0×107 g/(mol.h)。     

Recycling of methylaluminoxane (MAO) cocatalyst in ethylene polymerization with supported metallocene catalyst

The economy of the metallocene catalyst system in olefin polymerization depends more on the cost of methylaluminoxane (MAO) cocatalyst rather than on the catalyst cost since high ratio of cocatalyst to catalyst is required to have sufficient activity. The conditions to minimize the consumption of MAO have been studied for the ethylene polymerization with supported metallocene catalyst. By introducing the prepolymerization step, in which the supported metallocene catalyst is activated at high MAO concentration before polymerization, the MAO could be recovered after the prepolymerization and recycled repeatedly for the subsequent activation with marginal decrease in activity. No extra MAO was needed during the main polymerization. The addition of small amount of MAO or less expensive alkylaluminum at each recycle step kept the catalyst activity to the initial level. It compensates the MAO losses occurring both by the incomplete decantation of MAO solution and by the reaction with metallocene complex or impurities. As a result, the actual consumption ratio of Al/Zr in moles in commercial applications could be reduced to about 30 without sacrificing the activity. This value is significantly low considering that conventionally an Al/Zr ratio of 1,000 is required for sufficient activity. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

Bulk polymerization of vinyl chloride with half-titanocene/MAO catalyst

Bulk polymerization of vinyl chloride (VC) with Cp^∗Ti(OPh)₃/MAO catalyst was investigated. The bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst proceeded to give poly(vinyl chloride) (PVC) with high molecular weight in good yields. The M_n of the polymer increased in direct proportion to polymer yields and the line passed through the origin. The M_w/M_n of the polymer decreased with an increase of polymer yield. The GPC elution curves were unimodal and the whole curves shifted clearly to the higher molecular weight as a function of reaction time. This indicates that the control of molecular weight can be achieved in the polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst even in bulk. The structure of PVC obtained from the bulk polymerization of VC with Cp^∗Ti(OPh)₃/MAO catalyst consists of a regular structure. The thermal stability of the polymer obtained with Cp^∗Ti(OPh)/MAO catalyst was higher than that of PVC obtained from radical polymerization and depended on the molecular weight of the polymer. In contrast to that, the initial decomposition temperature of the polymer obtained from a radical polymerization did not depend on the molecular weight. We presumed that the decomposition of the polymer obtained with Cp^∗Ti(OPh)₃/MAO catalyst initiated at the chain end.     

Visualization of local ethylene polymerization activity on a flat CrO x /SiO2/Si(100) model catalyst

Flat model catalysts give access to fundamental aspects of olefin polymerization over heterogeneous catalysts. They are especially suited for the investigation on the early stages of polymer film growth employing scanning probe and electron microscopy. The polymerization centers are confined to a well defined two dimensional plane that remains constant during the polymerization. Using the Phillips (CrO _x /SiO₂) catalyst as an example we demonstrate how this approach can be used do visualize the lateral distribution of polymerization activity in the initial stages of polymer growth.     

Copolymerization of ethylene/1-hexene with zirconocene/MAO catalyst supported on spherical zirconia modified with BCl3, SiCl4, and glycerol

The spherical zirconia modified with BCl₃, SiCl₄, and glycerol was used as the support for rac-Et(Ind)₂ZrCl₂ catalyst to catalyze the copolymerization of ethylene/1-hexene. It is aimed to investigate the modification effects from different modifiers on copolymerization behaviors and compare the results with the unmodified system. The modified supports show higher activity than the unmodified one. Especially, the SiCl₄ modification exhibited the highest activity and produced copolymer with the largest 1-hexene insertion. This can be attributed to stronger interaction between the support and MAO along with the presence of SiCl₄ as a spacer group resulting in the absence of induction period. The modification did not affect the copolymers microstructure and the random copolymers were obtained from all supported systems. The narrower molecular weight distribution can be obtained from the modified supports. Besides, BCl₃ modification presents the highest molecular weight of polymer probably due to BCl₃ suppressing chain transfer reactions.