Study on the distribution of active centers in novel low Ti-loading MgCl2-supported Ziegler-Natta catalyst

Novel MgCl2-supported Ziegler-Natta (Z-N) catalysts prepared using a new one-pot ball milling method can effectively control the amounts of Ti-loading in the catalysts. Complex GPC data on polypropylene synthesized by these novel catalysts were analyzed using the method of fitting the molecular weight distribution (MWD) curves with a multiple Flory-Schulz function. It was found that multiple active centers exist in these novel catalysts. Detailed study of the effects of the Ti-loadings in the catalysts on the distribution of the active centers showed that the Ti-loadings in the novel MgCl2-supported Z-N catalysts might affect the proportion of each type of active centers; and might be the main factor responsible for the effect of the Ti-loadings on the microstructure, the molecular weight and molecular weight distribution width of the resultant polymer, the catalytic activity and polymerization kinetics.

EFFECTS OF EXTERNAL DONOR ON ACTIVE CENTER DISTRIBUTION OF SUPPORTED ZIEGLER-NATTA CATALYST

The composition distribution (CD) and microisotacticity distribution (ID) of propene/1-hexene copolymer synthesized by MgCl2/DIBP/TiCl4 (DIBP: diisobutyl phthalate) were determined by fractionating the copolymers according to crystallinity and characterizing the fractions by (CNMR)-C-13. The effects of two alkoxysilane donors, triethoxyphenylsilane (PTES) and dimethoxydi-tert-butylsilane (TBMS), on CD and ID of the copolymers were compared. Three main parts in the CD diagram of each copolymer were distinguished, which were correlated to active center distribution (ACD) based on three groups of different active centers. By studying the changes in l-hexene content, microisotacticity and reactivity ratio product of three typical fractions, the effects of external donor on ACD were better elucidated. It was found that TBMS shows much stronger effects on ACD than PTES. In the former system, most fractions were produced on active centers with relatively lower r(1)r(2), higher reactivity to I-hexene, and higher stereospecificity as compared to the system without external donor. It is concluded that the observed very extensive changes in ACD are mainly resulted by the formation of new types of active centers, possibly by coordination of external donor to certain positions on the catalyst.

DEPENDENCE OF THE DISTRIBUTION OF ACTIVE CENTERS ON MONOMER IN SUPPORTED ZIEGLER-NATTA CATALYSTS

Distribution of active centers(ACD)of ethylene or 1-hexene homopolymerization and ethylene-1-hexene copolymerization with a MgCl_2/TiCl_4 type Z-N catalyst were studied by deconvolution of the polymer molecular weight distribution into multiple Flory components.Each Flory component is thought to be formed by a certain type of active center. ACD of ethylene-1-hexene copolymer with very low 1-hexene incorporation was compared with that of ethylene homopolymer to see the effect of introducingα-olefin on ethyle...

Synthesis of PE with Broad MWD Catalyzed by Supported Ziegler-Natta Catalyst Consisting of Cycloalkoxy Silane as IED

Two kinds of cycloalkoxy silane compounds were synthesized and used as the internal electron donors （IEDs） of supported Ziegler-Natta catalyst for ethylene polymerization to produce polyethylene with broader molecular weight distribution （MWD）, The effect of the structure and the amount of these IEDs on the polymerization performance was in- vestigated. The results implied that the molecular weight distribution of the obtained polyethylene could be adjusted by the incorporation of IEDs. SEM result showed that the morphology of catalyst particle was spherical and uniform in size distribution. The titanium content of these catalysts was higher, the active TiCl4 species were easily anchored on the support than that without adding IED, which was determined by ICE The GPC result confirmed that the polyethylene with broader molecular weight distribution in the range of from 23.4 to 25.6 was obtained using triethoxy-（-cyclopentyloxy）-silane （ED1） and triethoxy-（-cyclohexyloxyl）- silane （ED2） as the internal electron donors.

Bis(trifluoromethylsulfonyl)phenylamines as Internal Donors for Ziegler-Natta Polymerization Catalysts

Several bis（trifluoromethylsulfonyl）phenylamines have been synthesized and used as internal donors for the preparation of heterogeneous Ziegler-Natta catalysts for propylene polymerization. These new cata- lysts are highly active and stereospecific in combination with an external donor for the polymerization of propylene. The activity of these catalysts is dramatically influenced by the electronic capability of the phenyl substituents on the sulfonyl phenylamines. Therefore, the performances of the catalysts can be modified by adjusting the electronic property of the phenyl substituents of the sulfonyl phenylamines.

COPOLYMERIZATION OF PROPYLENE WITH HINDERED PIPERIDINE MONOMER OVER A HIGH ACTIVITY SUPPORTED ZIEGLER-NATTA CATALYST

Copolymerization of propylene and hindered piperidine monomers was carried out over a high activity supported Ziegler-Natta catalyst, using Al(C2H5)(3) as cocatalyst. Factors which affect the copolymerization were studied, The copolymers exhibited high light stability without adding extra light stabilizers. A self-stabilized polypropylene was prepared.

STUDY ON 1-HEXENE POLYMERIZATION BASED ON ZIEGLER-NATTA CATALYSTS WITH DOPED SUPPORT

A series of Ti/Mg supported catalysts are prepared by using ball-milled mixtures of MgCl2-ethanol adducts and NaCl as supports, and 1-hexene polymerizations catalyzed by the novel catalysts are studied. It is found that the molecular weight distribution of poly(1-hexene) becomes apparently narrower when catalysts with doped supports are used, indicating that changing the structure of the support is an effective way to regulate the active center distribution of heterogeneous Ziegler-Natta catalyst.

Preparation of Ultra-High Molecular Weight Polypropylene Using Ziegler-Natta Catalyst via Combining Internal Electron Donor and Cocatalyst Loading

Due to the development of the new energy industry,polypropylene with ultra-high molecular weight plays a crucial role for battery isolation membrane.This work investigated the effect of internal electron donor of Ziegler-Natta catalyst system on the molecular weight of the obtained polypropylene.The scanning electron microscope(SEM)and Canon camera were used to characterize the surface morphologies of catalyst particles and polymer particles,respectively.Compared with the polypropylene particles featuring a spherical shape,these study results confirmed that the morphology duplication theory from the catalyst particle to the morphology of polymer particle was exhibited.The gel permeation chromatography(GPC)results revealed that the obtained polypropylene has a much higher average molecular weight than those prepared by conventional method.The Fourier transform infrared spectrometry(FT-IR)and X-ray photoelectron spectroscopy(XPS)revealed that the carbonyl oxygen atom on ester group was preferentially bound to Mg and Ti,as compared to the ether oxygen atom.The XPS results showed that the ratio of Ti^(3+)/Ti^(4+)could be changed by internal electron donors.When Ti3+content was nearly 99%in the Ziegler-Natta catalyst system,isotactic polypropylene with an ultra-high molecular weight of up to 1.42×10^(6)g/mol was obtained by Cat.3.This result implied that internal electron donor ID3 could reduce theβ-hydride elimination reaction to further increase the molecular weight of the obtained polymer.

Study of a Novel Fourth-generation Supported Ziegler-Natta Catalyst for Propylene Polymerization: Relationship between Catalyst Structure and Polymerization Properties

This article presents a detailed structural study of a new spherical Mg Cl2-supported Ti Cl4 Ziegler-Natta catalyst for isotactic propylene polymerization, and researches on the relationship between catalyst structure and polymer properties. The spherical support with the chemical composition of CH3CH2 OMg OCH(CH2Cl)2 has been synthesized from a new dispersion system and is used as the supporting material to prepare Ziegler-Natta catalyst. The XRD analysis indicates that the catalyst is fully activated with δ-Mg Cl2 in the active catalyst. The far-IR spectrometric results confirm again the presence of δ-Mg Cl2 in the active catalyst. Textural property of the active catalyst exhibits high surface area coupled with high porosity. The high activity in propylene polymerization is mainly ascribed to the full activation and the porous structure of the catalyst. Scanning electron microscopy/energy dispersive spectrometer mapping results indicate a uniform titanium distribution throughout the catalyst particles. Particle size analysis shows that the catalyst has a narrow particle size distribution. The perfect spherical shape, uniform titanium distribution and narrow particle size distribution of the catalyst confirm the advantage of polymer particles production with less fines. The solid state 13 C NMR and mid-IR spectroscopic analyses indicate that there exists strong complexation between diisobutyl phthalate and Mg Cl2, which leads to the high isotacticity of polypropylene.

STUDY ON THE MECHANISM OF 1-OCTENE ZIEGLER-NATTA POLYMERIZATION BASED ON THE NUMBER OF ACTIVE CENTERS

The number of active centers (C_p)-t and k_p-t profiles of Solvay type TiCl_3 - AlR_3 (R=C_2H_5, i-C_4H_9) or Stauffer AA TiCl_3-Al (C_2H_5)_3 catalyzed 1-octene polymerization were determined by using an acetyl chloride quenching method as well as kinetic data. The results show that in the studied systems k_p decreases when C_p increases, indicating the presence of two or more types of different active centers. The C_(p^(-t)) plots of the Solvay TiCl_3-AlR_3 systems show the presence of both stable active centers and unstable centers which decay in the polymerization process. The phenomena are explained based on a model of active center plurality. The increases of C_p in the induction periods are also discussed.

A New Method for Dissolving MgCl_2 for Preparation of Ziegler-Natta Propylene Polymerization Catalysts

A new method for the activation of crystalline magnesium chloride by polyethylene glycol was described. Polyethylene glycol could solubilize crystalline magnesium chloride. The resulting solution was used for the preparation of Ziegler-Natta propylene polymerization catalysts. These catalysts are highly active and stereospecific. The relationship between the catalytic activity and the Al/Ti ratio was studied in detail.

POISONING OF ACTIVE SITES ON ZIEGLER-NATTA CATALYST FOR PROPYLENE POLYMERIZATION

The effects of poisoning materials on catalytic activity and isospecificity of the supported Ziegler-Natta catalyst were investigated.A minor amount of simple structure of Lewis base,i.e.,methanol,acetone,ethyl acetate,was introduced into the catalyst slurry for partial poisoning catalytic active centers.It was found that the variations in deactivation power were in the order of methanol>acetone>ethyl acetate.The kinetic investigation via stopped-flow polymerization showed that poisoning compounds cau...

EFFECTS OF REACTION AND PROCESSING PARAMETERS ON ETHYLENE POLYMERIZATION USING DIFFERENT ZIEGLER-NATTA CATALYSTS:EMPLOYMENT OF TAGUCHI EXPERIMENTAL DESIGN AND RESPONSE SURFACE METHOD

Different Ziegler-Natta catalysts were employed to polymerize ethylene. To investigate the influences of reaction parameters, namely Al/Ti molar ratio, hydrogen and processing parameters, i.e. ethylene pressure and temperature, a Taguchi experimental design was worked out. An L27 orthogonal array was chosen to take the above-mentioned parameters and relevant interactions into account. Response surface method was the tool used to analyze the experimental design results. Al/Ti, ethylene pressure and temperature were selected as experimental design factors, and catalyst activity and polymerization yield were the response parameters. Increasing pressure, due to an increment in monomer accessibility, and rising Al/Ti, because of higher reduction in the catalysts, cause an increase in both polymerization yield and catalyst activity. Nonetheless, a higher temperature, thanks to reducing ethylene solubility in the slurry medium and partially catalyst destruction, lead to a reduction in both response parameters. A synergistic effect was also observed between temperature and pressure. All catalyst activities will reduce in the presence of hydrogen. Molecular weight also shows a decline in the presence of hydrogen as a transfer agent. However, the polydispersity index remains approximately intact. Using SEM, various morphologies, owing to different catalyst morphologies, were seen for the polyethylene.

乙丙共聚Ziegler-Natta钒系催化体系活化剂研究进展

乙丙橡胶钒系催化体系因其所制备产品序列分布均匀、结晶度低、组成分布较窄等优势,广泛应用于国内外乙丙橡胶生产企业。然而,钒系催化剂存在热稳定性差、活性中心寿命短、催化剂失活较快等问题,极大地降低了催化效率,提高了生产成本。为了实现降本增效,利用活化剂使得已经失活的钒系催化剂再活化,是工业上提高乙丙橡胶钒系催化剂活性的主要手段。本文综述了活化剂在国内外乙丙橡胶钒系催化体系应用方面的研究进展以及活化剂的加入对乙丙共聚反应活性以及所制备乙丙橡胶性能的影响,总结了活化剂在钒系催化体系中的活化机理。

醇镁加合物载体在Ziegler-Natta催化剂中的应用进展

基于醇镁加合物载体(简称醇镁载体)的Ziegler-Natta(Z-N)催化剂具有颗粒形貌优良、活性高等特点,醇镁载体的特性对催化剂和聚合物的综合性能有显著影响,是目前聚烯烃领域中的研究热点。介绍了氯化镁载体的发展历程以及醇镁载体的制备方法,分析了不同醇镁比、醇种类对醇镁载体结构的影响,综述了醇镁载体在Z-N催化剂中的应用,并对烯烃聚合用醇镁载体的开发提出了展望。

Ziegler-Natta催化剂活性中心的研究进展

Ziegler-Natta(Z-N)催化剂活性中心对催化剂和聚合物的性能具有重要影响,开展活性中心结构的研究将为催化剂结构和性能关系、催化机理等提供更深入的认识,是目前聚烯烃催化剂领域中的研究热点。介绍了不同谱学手段对活性中心的表征及对活性中心结构变化的原位监测,综述了通过构建模型催化剂并结合表面分析对活性中心结构进行模拟的研究,以及基于氯化镁晶体模型对活性中心结构的密度泛函理论计算研究,并对Z-N催化剂活性中心结构研究的发展方向进行了展望。

两种丙烯聚合用球形Ziegler-Natta催化剂的性能研究

采用扫描电子显微镜、激光粒度仪、密度仪和熔体流动速率仪(MFR)等研究了2种丙烯聚合用球形齐格勒-纳塔(Ziegler-Natta)催化剂(记为1#和2#)的性能。结果表明:与2#相比,1#的平均粒径更小,粒径分布更宽,活性更高,对氢气更敏感,且所得聚丙烯(PP)堆积密度更高,但PP颗粒粒径较小。不同外给电子体对丙烯聚合的影响不同。采用二环戊基二甲氧基硅烷为外给电子体时,2种催化剂活性均最高,所得PP的MFR均最小。

孔道结构修饰的Ziegler-Natta催化剂设计与高抗冲低缠结UHMWPE的制备

从SiO_(2)载体孔道修饰的角度出发,向多级孔道中同时引入聚苯乙烯(PS)和聚倍半硅氧烷(POSS),形成功能化复合载体,并用于负载TiCl4,制备SiO_(2)/PS/POSS/TiCl4负载型催化剂。采用热重分析、N2等温吸附脱附、扫描电镜、漫反射红外光谱等手段对修饰前后催化剂的结构进行表征,发现利用苯乙烯的原位聚合能够向SiO_(2)多级孔道,尤其是微孔中引入PS,孔道内PS链段的溶胀行为导致聚合时乙烯传质阻力增大,聚合活性降低。向SiO_(2)多级孔道中引入POSS,由于POSS分子的空间位阻,其只能进入SiO_(2)大孔中,初生态聚乙烯分子链缠结程度降低有限。而将PS与POSS共同引入催化剂各级孔道中,PS与POSS能够产生良性协同作用,能够以高活性制备低缠结的超高分子量聚乙烯,显著提升了产品的抗冲击强度。最后通过降低孔道内TiCl_(4)的负载量,进一步稀释催化剂活性中心,实现聚乙烯活性链解缠结的过程强化。当钛含量降至2.65%时,聚合活性、抗冲击强度和链缠结程度均达到最佳。

丙烯聚合用Ziegler-Natta催化剂预聚合的研究进展

综述了丙烯聚合用Ziegler-Natta催化剂预聚合的研究进展,包括预聚合对催化剂的影响、预聚合方法及其应用。预聚合可以提高催化剂活性、改善聚合物的颗粒形态、影响聚合动力学行为。现有研究已经开发了不同的预聚合方法,进一步改善了催化剂和聚合物的颗粒形态,提高了聚合物的性能。经过预聚合制备的预聚合催化剂,适用于无预聚合操作单元的气相丙烯聚合工艺,不仅能有效解决聚合物中细粉含量高、聚合物结块等问题,还能获得具有高性能、高附加值的聚丙烯产品。

PE-UHMW聚合用氧基硅烷内给电子体Ziegler-Natta催化剂的制备及应用

采用实验室自制的两种复合型氧基硅烷内给电子体:二甲基二(2-酚基乙氧基)硅烷(IED1)和二甲基二(2-氯乙氧基)硅烷(IED2),将两种内给电子体配置Ziegler-Natta催化剂并进行乙烯的催化聚合以制备超高分子量聚乙烯(PE-UHMW)。考察了两种内给电子体加入对Ziegler-Natta催化剂的载钛量、催化剂活性、催化剂的微观形貌及聚合物分子量等因素的影响,并考察催化剂加入量、聚合温度、聚合时间、助催化剂加入量对PE-UHMW聚合效果的影响。由于IED1结构中含有4个含氧基团,电子云密度高于IED2,因此IED1对催化剂活性以及聚合物分子量影响较大。最终确定PE-UHMW聚合工艺条件为:以IED1为内给电子体,催化剂加入量为12 mg/L,IED1与载体氯化镁的物质的量之比为1∶4,聚合温度为75℃,聚合时间为2 h,催化剂中Al/Ti物质的量之比为80。在此工艺条件下催化剂的催化效率为17.1 kg/(g·h),催化剂载钛量为5.8%,PE-UHMW堆密度为0.3 g/cm^(3),PE-UHMW分子量为4.0×10^(6)。