Catalyseurs Ziegler-Natta supportés sur MgCl2 pour la polymérisation du propène. I. Etude de la réaction entre le triéthylaluminium et le benzoate d'ethyle

In this article we describe a study of the reaction between triethylaluminium (TEA) and ethylbenzoate (BE) in a heptane solution by Fourier transform, infrared (IR), and ultraviolet (UV) spectroscopy. These compounds were chosen as a model of the cocatalytic solution used with a Ziegler-Natta catalyst supported on MgCl₂ for the stereospecific polymerization of propene. In the polymerization concentration range a 2 TEA:1 BE yellow complex was added to the solution and no free BE could be detected at a AI/BE molar ratio above 2: the solution contained only free and complexed TEA. The complex decomposed spontaneously to a colorless aluminium alcoholate. The rate of decomposition remained slow at room temperature and the reaction was enhanced by heating or by a high AI/BE ratio or high AI concentration. The decomposition was inhibited in the presence of an olefin.     

Catalyseurs Ziegler-Natta supportés sur MgCl2 pour la polymérisation stéréorégulée du propène. III. Systèmes catalytiques à hautes performances comprenant un solide ternaire: MgCl2, ester aromatique,TiCl4

An examination of the precatalyst which contains three compounds (MgCl₂–TiCl₄-aromatic ester) uncovered numberous properties that apparently are common to all precatalysts and have already been observed in the simpler systems: a continous decrease in the polymerization rate during polymerization, characterized by a deactivation index that does not depend on the precatalyst but only on the cocatalyst; isotacTiClty control by the [AI]/[aromatic ester] ratio in the cocatalytic solution; and fast and reversible control of kinetics and tacTiClty by the same ratio. The precatalyst prepared by impregnation of the aromatic ester in MgCl₂ or MgCl₂–TiCl₄ presents moderate or no improvement when compared with the simpler MgCl₂–TiCl₄ catalysts. The yellow precatalyst prepared by milling MgCl₂ with the aromatic ester and impregnating with TiCl₄ are the only products that provide high activity and isotactic index above 95% simultaneously, as revealed by the patent literature. Interpretation of the role played by the electron donor, based on infrared studies, are proposed: in the precatalyst it controls fixation of TiCl₄ on MgCl₂; in the cocatalytic solution it regulates the isospecificity of the active site by contact with the alkylaluminium-aromatic ester complex and slows polymerization. Free electron donor gradually poisons the active centers.     

Chlorotitanium (IV) tetradentate Schiff‐base complex immobilized on inorganic supports: Support type and other factors having effect on ethylene polymerization activity

A titanium complex with [O,N,N,O]‐type tetradentate Schiff base (LTiCl₂), never used before in polymerization of olefins, was immobilized on silica‐ and magnesium‐type carriers, and it was used in ethylene polymerization. The conducted research revealed that the catalytic properties of the complex LTiCl₂ supported on those carriers were different for both the catalytic systems studied, and simultaneously they turned out different from those of the unsupported system. The supported catalysts require the use of Me₃Al, Et₃Al, or MAO as the activator to be able to offer high catalytic activities, whereas Et₂AlCl is needed for the nonsupported catalyst. This finding, together with considerable changes in polymerization yields and in properties of polymers versus composition of the catalytic system, suggest that there are different types of active sites in the studied catalysts. The catalyst anchored on the carrier produced in the reaction of MgCl₂·3.4EtOH with Et₂AlCl is definitely the most active one within the support systems tested. Its activity remarkably increases with the increasing reaction temperature. Moreover, that catalyst does not undergo deactivation over the studied period of time, irrespective of the type of the activator used and of the process temperature. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4811–4821, 2009     

Novel spherical Ziegler–Natta catalyst for polymerization and copolymerization. I. Spherical MgCl2 support

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     

Superactive and stereospecific catalysts. II. Kinetics of propylene polymerizations

The kinetics of propylene polymerization by superactive CH-catalyst prepared from toluene solution of MgCl₂ · EH/PA/TiCl₄–TEA/PES was investigated. The results are compared with CW-catalyst prepared from crystalline MgCl₂/EB/PC/TEA/TiCl₄–TEA/MPT (abbreviations given in the text). The former is four times more active than the latter and produces more isotactic polypropylene. The CH-catalyst has 25% of the Ti as isospecific sites as compared to 6.7% for the CW-catalysts. These sites have the same rate constant of propagation so that the higher polymerization activity of the CH-catalyst is attributable simply to a greater number of active sites. Differences in the kinetics of deactivation and of chain transfer for the two catalysts are described.     

Characterization of the changes in the initial morphology for MgCl2-supported Ziegler-Natta polymerization catalysts

Recently considerable detail has become available on the initial morphology and the morphological changes that occur for silica based Cr catalysts for ethylene polymerization. These catalysts are produced as a dry powder and may be employed either in gas phase or in slurry processes. MgCl₂-supported Ziegler-Natta polymerization catalysts are often prepared and employed as slurries. They usually are never dried and thus few studies have employed the spectra of physical techniques common to the characterization of pore structure. In the current study, we have carefully removed the solvent for both ball-milled and precipitated MgCl₂-supported catalysts. These catalysts are characterized by physical sorption, mercury porosimetry, and electron microscopy both as prepared and during the initial stages of polymerization (to ～ 100 g of polymer/g of catalyst). We find that the initial catalyst may be represented by a complex agglomerate of small crystallites as contrasted with the branched pore network found in Cr/silica catalysts. As a result, it is concluded that the initial fragmentation of the MgCl₂ based systems is more uniform as contrasted with the progressive fragmentation of the silica-based system. This fragmentation mechanism facilitates the retention of greater polymer/catalyst surface during the initial stages of the polymerization. © 1992 John Wiley & Sons, Inc.     

Vanadium Modification Effects on the (SiO2/MgO/MgCl2)•TiClx Ziegler–Natta Polyethylene Catalyst

A novel vanadium‐modified (SiO₂/MgO/MgCl₂)·TiCl_x Ziegler–Natta ethylene polymerization catalyst with much better catalytic performance is successfully developed. The catalyst is prepared by co‐impregnation of aqueous solution of water‐soluble magnesium and vanadium compounds on SiO₂, and a supported thin layer of magnesium and vanadium oxides is formed over the surface of SiO₂ after high temperature calcination in dry air, followed by further reaction with titanium tetrachloride to synthesize the magnesium dichloride carrier in situ and to support the titanium species simultaneously. By characterization of the catalysts and the polymers and investigation of the polymerization behaviors, it is found that compared with the original (SiO₂/MgO/MgCl₂)·TiCl_x ZN catalyst, the introduction of vanadium species induce improved catalytic performance with 27% higher activity, 48% higher hydrogen response, and 60% higher 1‐hexene incorporation ability with better short chain branch distribution.

     

Stereospecific polymerization of isobutyl vinyl ether by AIR3–VCl3·LiCl catalyst. II. Effects of polymerization conditions on polymerization

The effect of polymerization conditions such as aging time of the catalyst, polymerization temperature, polymerization time, monomer concentration, and catalyst concentration on the polymerization of isobutyl vinyl ether was intensively studied by using the VCI₃·LiCl–Al(i-Bu)₃ system at an Al(i-Bu)/VCl₃·LiCl ratio of 6 at which the cationic polymerization by VCl₃·LiCl is sufficiently depressed. About 10 min aging of the catalyst in the presence of monomer yields a fairly stable catalytie system. The optimum polymerization temperature is around 30°C. The conversion increased with increasing monomer concentration, whereas the stereospecificity of polymerization decreased. Unexpectedly, the conversion decreased as total catalyst concentration increased. This phenomenon is explained by considering the deactivation of catalytic sites by the excess of Al(i-Bu)₃. A reasonable mechanism from kinetic considerations is that two molecules of Al(i-Bu)₃ deactivate the catalytic site in an equilibrium reaction. This deactivation is understandable by considering that the coordination of two molecules of Al(i-Bu)₃ will occupy all the coordination positions of vanadium, so that there is no room for coordination of monomer coming to the catalytic site.     

New penta-ether as the internal donor in the MgCl2-supported Ziegler-Natta catalysts for propylene polymerization

The penta-ether compound was synthesized by the reaction of di(trimethylolpropane) with sodium hydride as the strong base and methyl iodide as the alkyl halide. This compound was characterized by NMR, FTIR, and GC techniques. The MgCl₂-supported titanium catalysts were incorporated with varying amounts of penta-ether compound as the internal donor and also the catalysts without the internal donor were synthesized. The synthesized catalysts and the conventional Ziegler- Natta catalyst were characterized. The titanium contents were determined by spectrophotometry, magnesium by complexometric titration and chloride by argentometric titration. The effects of the new internal donor on propylene polymerization with the prepared MgCl₂-supported Ziegler-Natta catalysts were investigated and then these results were compared to the results obtained using the conventional diisobutyl phthalate-besed-Ziegler-Natta catalyst. The highest crystallinity degree, melting temperature, and isotacticity of polypropylene were obtained using the catalyst with a penta-ether/Mg molar ratio equal to 0.21.     

Kinetic behavior of ethylene/1‐hexene copolymerization in slurry and solution reactors

The copolymerization of ethylene and 1‐hexene over a spherical polymer/MgCl₂‐supported TiCl₄ catalyst was studied as a function of the polymerization temperature from 40 to 100 °C in a slurry reactor and from 120 to 200 °C in a solution reactor with triethylaluminum (TEA) as a cocatalyst (1.0–6.8 mmol). The activities increased from 40 to 80 °C and then declined monotonically with increases in the temperature during the slurry and solution polymerizations. The kinetic behavior in the slurry and solution operations was described by the same rate expression. The modeling results indicated that the catalyst had at least two different types of catalytic sites; one site was responsible for the acceleration–decay nature of the activity profiles, whereas the second site resulted in long‐term activity. The apparent activation energy for site activation in the slurry operation was 69.9 kJ/mol; no activation energies for site activation could be estimated for the solution operation because the activation process was essentially instantaneous at the higher temperatures. The activation energies for deactivation were 100.3 kJ/mol for the slurry operation and 31.2 kJ/mol for the solution operation. The responses to TEA were similar for the slurry and solution operations; the rates increased with increasing amounts of TEA between 1.0 and 3.4 mmol and then decreased with larger amounts of TEA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2248–2257, 2005     

Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride immobilized on MgCl2‐based supports as a highly effective precursor for ethylene polymerization

Ethylenebis(5‐chlorosalicylideneiminato)vanadium dichloride supported on MgCl₂(THF)₂ or on the same carrier modified by Et_nAlCl_3?n, where n = 1–3, was used in ethylene polymerization in the presence of MAO or a common alkylaluminium compounds as a cocatalyst. The support type alter vanadium loading and also change the characteristic of the catalytic active sites. Et₂AlCl is the best activator for a catalyst which has been immobilized on a nonmodified support, whereas the systems which contain a carrier which has been modified by an organoaluminium compound reveal the highest activity in conjunction with MAO. That difference, together with different temperature effects on polymerization efficiency (i.e., decrease and increase of catalytic activity for increasing temperatures, respectively) suggest the formation of different types of active sites in the catalytic systems supported on modified and nonmodified magnesium carrier. However, all supported precatalysts possess a long lifetime, still being active towards ethylene polymerization after 2 h. All the systems yield wide MWD polyethylene, while bimodal MWD is found for some part of analyzed samples. Polyethylene with bimodal particle size distribution is formed with the system which contain modified carriers at higher temperatures. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3480–3489, 2009     

Active center determinations on MgCl2‐supported fourth‐ and fifth‐generation Ziegler–Natta catalysts for propylene polymerization

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     

Hydrogen Effects for Propylene Polymerization with Ultra Low TiCl3 Loading MgCl2-Supported Catalyst

Hydrogen effects for propylene polymerization were investigated with ultra low TiCl₃ loading MgCl₂-supported catalysts in which the electric states of Ti species can be almost uniform. Hydrogen did not affect the catalyst activity, while the efficiency of hydrogen as a chain transfer agent was found to depend on the Ti content of the catalyst and the stereospecificity of the polymerization sites: Hydrogen was effective for isospecific sites independent of Ti contents, but inert for aspecific sites only at the extremely low Ti content. These results were explained within the island model, where isospecific sites may be located in the islands with other Ti species in their surroundings acting, as a steric hindrance for isospecific polymerization and as hydrogen dissociation sites after deactivation. Most of the aspecific sites should be isolated only at the extremely low Ti content. These isolated sites have no other Ti species in their surroundings, i.e. no hydrogen dissociation sites, and are inert to hydrogen.     

Preparation of polypropylene/clay nanocomposites by <Emphasis Type="Italic">in situ</Emphasis> polymerization with TiCl<Subscript>4</Subscript>/MgCl<Subscript>2</Subscript>/clay compound catalyst

TiCl₄/MgCl₂/clay compound catalyst was prepared by chemical reaction.Exfoliated polypropylene（PP）/clay nanocomposites were synthesized by in situ polymerization with this compound catalyst.Effects of polymerization temperature,polymerization time,propylene pressure,solvent consumption and pre-treat time of catalyst on catalyst activity and catalytic stereospecificity were studied.Under optimal conditions,activity of the nano-compound catalyst is about 88.3 kg/（mol Ti·h）.Isotacticity of PP obtained in the nanocomposites is in the range of 89%-99%,and its melting temperature is about 159℃.The weight-average molecular weight of PP can reach 6.7×10⁵ - 7.8×10⁵,and the molecular weight distribution is between 7.7 and 7.9.     

TiCl4/XROH/MgCl2/Et3Al催化剂合成宽分子量分布乙烯/1-己烯共聚物

采用MgCl₂负载TiCl₄及1,3-二氯-2-丙醇给电子体(XROH),与三乙基铝助催化剂组成的催化剂体系,合成了1-己烯共聚率高且宽分子量分布的乙烯/1-己烯共聚物。 讨论了催化体系的组成、配比和聚合条件对乙烯/1-己烯共聚合行为,共聚物结构、分子量及分子量分布的影响。 结果表明,n(Ti)∶n(Mg)=10∶1,n(XROH)∶n(MgCl₂)=2.6∶1,n(Al)∶n(Ti)=100∶1,乙烯压力0.45 MPa,聚合温度80 ℃,聚合时间2 h,共聚单体(1-hexene)浓度0.25 mol/L时,催化效率达23.2 kg/g cat。 采用¹³C NMR、X-ray、SEM、WAXD、DSC、GPC等测试技术对催化剂、共聚物的结构进行了表征。 结果表明,在Zieglar-Natta(Z-N)催化体系中,给电子体多卤代醇与TiCl4结合,载体MgCl2的晶体结构发生了变化。 结晶度降低,有利于催化剂负载量的提高(ω(Ti)=4.8%)和催化效率增大。 催化体系产生了多种活性中心,使聚烯烃分子量分布变宽(15~20)。 多卤代醇还可增强1-己烯与乙烯的共聚能力,在共聚物中1-己烯的摩尔分数达5.1%。     

Probing the roles of diethylaluminum chloride in propylene polymerization with MgCl2-supported ziegler-natta catalysts

In this article, the effect of diethylaluminum chloride (DEAC) in propylene polymerization with MgCl₂-supported Ziegler-Natta catalyst was studied. Addition of DEAC in the catalyst system caused evident change in catalytic activity and polymer chain structure. The activity decrease in raising DEAC/Ti molar ratio from 0 to 2 is a result of depressed production of isotactic polypropylene chains. The number of active centers in fractions of each polymer sample was determined by quenching the polymerization with 2-thiophenecarbonyl chloride and fractionating the polymer into isotactic, mediumisotactic and atactic fractions. The number of active centers in isotactic fraction ([C_i*]/[Ti]) was lowered by increasing DEAC/Ti molar ratio to 2, but further increasing the DEAC/Ti molar ratio to 20 caused marked increase of [C_i*]/[Ti]. The number of active centers that produce atactic and medium-isotactic PP chains was less influenced by DEAC in the range of DEAC/Ti = 0–10, but increased when the DEAC/Ti molar ratio was further raised to 20. The propagation rate constant of C_i* (k _pi) was evidently increased when DEAC/Ti molar ratio was raised from 0 to 5, but further increase in DEAC/Ti ratio caused gradual decrease in k _pi. The complicated effect of DEAC on the polymerization kinetics, catalysis behaviors and polymer structure can be reasonably explained by adsorption of DEAC on the central metal of the active centers or on Mg atoms adjacent to the central metal.     

Preparation and characterization of spherical PP/PB alloys with MgCl2-supported Ziegler-Natta catalyst

Polypropylene（PP）/polybutene-1（PB） alloys within reactor were prepared by MgCl₂-supported Ziegler-Natta catalyst with sequential two-stage polymerization technology.First,propylene homo-polymerizations were carried out to form isotactic polypropylene（iPP） particles containing active catalyst.Then,butene-1 was subsequently polymerized to form polybutene-1 phase inside the iPP particles.Finally,iPP/PB alloys with spherical shape and adjustable PB content were synthesized.The catalytic activity and catalytic stereospecificity of the Z-N catalyst in the two-stage polymerization process are discussed.The composition and physical properties of the PP alloys were characterized by FT-IR,¹³C-NMR,SEM,DSC and XRD.It was found that the in-reactor PP alloys are mainly composed of PP and PB with a little amount of poly（butene-co -propylene） random copolymers and poly（butene-block-propylene） block copolymers.SEM measurements verified that the PB phases with size in the range of 300-400 nm dispersed in the PP matrix uniformly.The incorporation of PB upon the PP matrix affects the properties of final products greatly.     

Magnesium chloride supported high-mileage catalysts for olefin polymerization. IV. FTIR and quantitative analysis of modifiers in the catalysts

Fourier transform infrared (FTIR) spectra were obtained for a typical MgCl₂-supported, high-mileage catalyst for propylene polymerization. When ball-milling MgCl₂ with ethyl benzoate (EB), the latter is incorporated into the support (I) by Lewis acid-base complexation involving both oxygen atoms of the ester. Reaction of (I) with p-cresol (PC) resulted in a material (II) that contains all the characteristic IR bands of PC. The reaction of (II) that contains all the characteristic IR bands of PC. The reaction of (II) with AlEt₃ (TEA) resulted in (III) whose spectrum supports the reaction observed by product analysis and NMR spectroscopy. There was no evidence of any reaction between TEA and EB. Further reaction of (III) with an excess of TiCl₄ caused substantial removal of the p-cresol moiety as shown by the diminution of its characteristic bands. Finally, activation with 3TEA-1MT (methyl-p-toluate) complexes gave spectra that revealed the presence of MT in the activated catalyst without any visage of p-cresol moiety. The nondestructive FTIR method, however, is not quantitative. Quantitative analysis of the organic components in the support materials (I), (II), and (III) and the catalysts was accomplished by hydrolysis of the inorganic components, extraction with ether, and analysis by gas chromatography. The results are in good agreement with composition deducted from elemental analysis and substantiate the FTIR conclusions.     

Direct observation of MgCl2‐supported Ziegler catalysts by high resolution transmission electron microscopy

The surface atomic structure of MgCl₂ crystalline particles and MgCl₂‐supported Ziegler catalysts was observed by means of high resolution transmission electron microscopy. Step‐terrace surface structures, characteristic of the structure of the MgCl₂ crystal, are found in the observed images of MgCl₂ particles. The observation of the structure of MgCl₂‐supported Ziegler catalysts shows that the MgCl₂ crystals are severely deformed by the processes of catalyst preparation. Due to the preparation procedure used the structure of the catalyst changes from crystalline to amorphous.     

The activation of MgCl2-supported ziegler-natta catalysts—II: Correlation between activity and structural disorder

The properties have been examined for Ziegler-Natta catalysts comprising TiCl₄ (Ti contents 2.0, 3.4 and 4.2%) supported on MgCl₂ activated by dry ball-milling up to 250 hr. The samples have been investigated by measurements of catalytic activity in polymerization, of surface area and of some structural parameters related to the crystal disorder introduced by ball-milling. It is shown that the TiCl₄ content affects the activation; a relationship has been found between the crystal disorder of the MgCl₂ support and the catalytic activity.