Catalytic activity and control of the nascent morphology of polyethylenes obtained with first and second generation of Ziegler–Natta catalysts

The morphologies of the as-produced polyethylenes obtained by slurry polymerization process of ethylene in n-heptane, using heterogeneous conventional and supported Ziegler–Natta catalysts, were investigated. The ability of four different catalytic systems in controlling the size and shape of the nascent polymer particles were tested. The catalytic systems employed were: the original Ziegler type catalyst produced by reduction of TiCl₄ with Et₂AlCl, the Natta type catalyst TiCl₃–AA, the reduced TiCl₄ with the metal carbonyls [Mo(CO)₆ and Mn₂(CO)₁₀], and the supported TiCl₄ on three commercial silicas having different surface areas: Davison 951, 952, and also the Dart 1000. It was found that the carriers affect the catalytic activity of the final catalyst and also its kinetic behavior. The supported Ziegler–Natta catalysts control more easily the nascent polymer particles (size, shape, and porosity) than the conventional ones. In addition the morphology of the catalysts and the subsequent polymer particles are closely related to the parent morphology of the silicas used as carriers. Furthermore, the nascent morphology of the polyethylenes obtained with the conventional TiCl₄–Et₂AlCl catalytic system can be modified by using different |Al|/|Ti| ratios, resulting in more dense, spherical, and bigger polymer particles by increasing this ratio. On the other hand, detailed studies on the texture or arrangement of the polymer particles reveal the existence of mainly two fine morphologies (globular and wormlike), which are the result of the order of the primary or elementary catalyst particles (microspheres and platelets), the force linking them together, and the activity of the polymerization centers placed on their surface.     

Highly active MgO-supported TiCl4 catalyst for the ethylene polymerization

Summary The MgO-supported TiCl₄ catalysts prepared by heating MgO with TiCl₄ showed a high activity for the ethylene polymerization in combination with Et₃Al or i-Bu₃Al. In these highly active catalysts, it has been shown that MgCl₂ is formed in the MgO-TiCl₄ reaction and is considered to contribute to the enhancement of the activity of the catalysts.     

Allene adsorption isotherms and active site determination on various titanium trichloride catalysts

The techniques of gas-solid chromatography and temperature programmed desorption have been applied to the problem of evaluating the number of active polymerizing centres in variously prepared titanium trichloride catalysts. Using gas-solid chromatography the adsorption isotherms of allene on (i) hydrogen reduced TiCl₄ (Stauffer H), (ii) aluminium reduced TiCl₄ (Stauffer AA), (iii) Et₂AlCl activated Stauffer AA and (iv) Et₃Al activated Stauffer AA, have been obtained. The non-linear isotherms so derived have been analysed in terms of a two site Langmuir model from which the heats of adsorption and the number of adsorption sites have been evaluated. The number of surface sites is virtually identical on all four materials having values of 4.2 × 10¹³, 5.3 × 10¹³, 4.8 × 10¹³ and 4.9 × 10¹³ sites cm^?2 respectively ($\text{～200}\text{A}\text{?}{}^2$ per site), the majority of these sites (> 90%) having heats of adsorption of 8 kcal mol^?1. Since these catalysts have different surface areas which varied from 2.5 m²g^?1 to 8.7 m²g^?1 the near identity of the site densities suggests that a fundamental property of the solid is being measured. The only observed effect of the aluminium alkyl activator on Stauffer AA was to reduce the heat of adsorption of the high energy site from 16.5 kcal mol^?1 to 12.7 kcal mol^?1 (Et₂AlCl) and to 9.3 kcal mol^?1 (Et₃Al). Temperature programmed desorption experiments on Stauffer AA and Stauffer H confirmed the heat of adsorption and the site densities of the high energy sites showing coverages of 2.9 × 10¹² and 2.6 × 10¹² sites cm^?2 respectively for these sites (identical to those predicted by the two site Langmuir adsorption model) and desorption activation energies of 18.8 and 17.8 kcal mol^?1 respectively, inferring no activation energy to adsorption on to these sites.     

Preparation of high isotactic polybutene‐1

Polymerization of butene‐1 (B‐1) was carried out with a PP‐TiCl₃/Et₂AlCl/methyl methacrylate (MMA) catalyst system in n‐heptane. The influence of temperature, pressure, time and H₂ on molecular weight, isotacticity, and catalytic activity were studied by viscometry, solubility in boiling diethyl ether, and measuring the polymer produced, respectively. The structural properties of the isotactic polybutene‐1 (IPB‐1) were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and melt flow index (MFI). The molecular weight of the products can be controlled by H₂. It was found that the catalyst showed high isotacticity and activity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2533–2539, 2000     

Studies on the polymerization of propylene using high activity ziegler-natta catalysts. 1: Kinetic models for rate decay in ziegler-natta polymerization

Kinetic models for describing the time dependence of the polymerization rate and active centre concentration for high activity Ziegler-Natta catalyst systems are discussed. It is demonstrated that the decay in the rate of polymerization and in the concentration of active centres with time for the polymerization of propylene with the heterogeneous catalyst system MgCl₂/EB/TiCl₄? Al(i-Bu)₃/EB can be represented better by a modified multi-centre first order decay model than by the other models which are considered.     

Electrophilic substitution of organosilicon compounds

Summary Quantitative electrophilic allylation of 2,4,4-trimethyl-2-chloropentane (TMP-Cl) a molecule which closely mimics the tert-chlorine termini of by allyltrimethylsilane (AllylSiMe₃) has been accomplished and the product 4,4,6,6-tetramethyl-1-heptene (TMP-allyl), a new organic compound, has been characterized by¹H NMR spectroscopy. The synthesis was carried out by the use of Et₂AlCl or TiCl₄ using CH₂Cl₂ or CH₃Cl or CH₂Cl₂-C₆H₁₄ solvent systems in the range from –70 to 0°C. The allylation efficiency sequence of the Lewis acids studied was: Et₂AlCl > TiCl₄ > SnCl₄ BCl₃. Varying the temperature from –70° to 20°C moderately affected the conversions with lower temperatures being preferable. A dramatic solvent effect was observed: While in the presence of 30% CH₂Cl₂ both allylation efficiency and rate were very high, in hexanes allylation was strongly retarded. Vinyltrimethylsilane (VinylSiMe₃), a potential vinylating agent, was inactive under the same conditions.     

Zur Wechselwirkung von Donoren mit Diethylaluminiumchlorid. IV. 13C-NMR-Untersuchungen zum Ausmaß der Komplexbildung

The Interaction of Donors with Diethyl Aluminium Chloride. IV. ¹³C-N.M.R.-Investigations on the Degree of Complex Formation Et₂AlCl has some importance for the initiation of cationic polymerizations where its activity can be influenced by the addition of donor compounds. To enlight the elementary processes quantitative ¹³C-n.m.r. spectroscopic investigations of the model systems Et₂AlCl/pyridine and piperidine, respectively, were carried out. Detailed information are given with regard to the molar ratios of acceptor and donors. The formation of an ionic intermediate complex was observed. The degree of complex formation is higher for piperidine than for pyridine. In the case of pyridine a 1:1 complex is formed. With piperidine a complexation with higher coordination must be assumed.     

Copolymerization of propylene with a small amount of ethylene using a MgCl2/TiCl4 and a TiCl3 catalyst system

Summary Copolymerization of propylene with a small amount of ethylene and homopolymerization of propylene were performed using a highly active MgCl₂/TiCl₄-Et₃Al/ethyl benzoate(EB) and a conventional TiCl₃-Et₂AlCl catalyst systems. The obtained polymers were fractionated into n-decane (C₁₀) soluble and insoluble portions. In all homopolymer fractions with the investigated catalyst systems and copolymer fractions with TiCl₃ catalyst system, the inversion of the direction of arrangement of the propylene unit was not observed by ¹³C-NMR analysis. On the other hand, in C₁₀ soluble fractions of copolymer using MgCl₂/TiCl₄ catalyst system, regardless of the presence of EB, a significant amount of the inversion unit was detected.     

Functionalization of polyethylene using borane reagents and metallocene catalysts

A new method to prepare functionalized polyethylene involving borane intermediates and transition metal catalysts is described. Two processes, direct and post polymerizations, were employed to prepare borane-containing polyethylene (PE-B), which can be transformed to functionalized polyethylene (LLDPE-f) with various functional groups, such as ? BR₂, ? OH, ? NH₂, ? OSi(CH₃)₃. In the direct process, the PE-B copolymers were prepared in one step by copolymerization of ethylene with a borane monomer (ω-borane-α-olefin). The post polymerization process requires two steps: copolymerization of ethylene and 1,4-hexadiene, and subsequential hydroboration reaction of unsaturated PE. Three transition metal catalysts, including two homogeneous metallocene (Cp₂ZrCl₂ [bis(cyclopentadienyl) zirconium dichloride] and Et(Ind)₂ZrCl₂ [1,1′-ethylenedi-η⁵-indenyl-zirconium dichloride] with MAO (methylaluminoxane)) and one heterogeneous (TiCl₃·AA/Et₂AlCl) ones, were studied in the copolymerization reactions. The single site Et(Ind)₂ZrCl₂/MAO homogeneous catalyst, with a strained ligand geometry and opened active site, is by far the most effective system in the incorporation of high olefins into polyethylene structures.     

Studies on probing SiO2 surface using BF3 as probe and SiO2/Al2Et3Cl3/TiCl4(PhMgCl) catalytic system for copolymerization of ethylene and propylene

Using BF₃ as probe, the surface of SiO₂ was probed. The effects of the roast temperature on the SiO₂ surface were investigated and a possible mechanism is suggested. Using SiO₂ as starting material for supports, new supported catalysts for copolymerization of ethylene and propylene were prepared and their possible structures are discussed. It was found that higher polymerization productivity, for instance, 480 kg P/mol_Ti h, can be obtained by using a SiO₂/Al₂Et₃Cl₃/TiCl₄ catalytic system and addition of PhMgCl to this catalytic system can significantly increase polymerization activity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1583–1589, 2000     

Synthesis and structural characterisation of some highly hindered N-functionalised organoamido complexes of titanium(IV) and zirconium(IV)

Treatment of the group 4 halides TiCl₄ and ZrCl₄ with various stoichiometries of [(6-Me-TMS-Apy)Li(Et₂O)] (6-Me-TMS-ApyH=2-(trimethylsilylamino)-6-methylpyridine) has been studied yielding [(6-Me-TMS-Apy)TiCl₃]₂ (1), [(6-Me-TMS-Apy)₃TiCl] (2) or [(6-Me-TMS-Apy)₃ZrCl] (3). The structures of compounds (1), (2) and (3) were characterised by spectroscopic and X-ray crystallographic methods. The X-ray structure of (1) is a centrosymmetric dimer through bridging chlorides. Compounds (2) and (3) are isostructural mononuclear complexes with seven-coordinate metal centres.     

Coordinate polymerization of heterocycles: 1. Oligomerization of epichlorohydrin by TiCl4

The polymerization of epichlorohydrin proceeds via the TiCl₄. 2EPC complex provided the concentration of epichlorohydrin is twice as high as that of TiCl₄. The oligomerization process requires supposedly the existence of a complex in which the epichlorohydrin is coordinate through a ClTi bond. Diethyl ether has an inhibiting effect on the reaction. The oligomerization rate is increased in the presence of acetyl chloride, diethyl ether having no effect this time. The transformation of epichlorohydrin to polymer is always kinetically non-stationary, the number of active centres decreasing with time. Both the initiation and propagation steps proceed through a rearrangement following the coordination of monomer to the activating ligands. No polymerization active free ions have been found to be present in the system. The intermediate and final products were analysed employing spectral, chromatographic, kinetic, and conductivity measurements. The reaction mechanism of oligomerization has been suggested.     

Particle control of Ziegler–Natta catalysts based on TiCl3 for propylene polymerization. Effect of prepolymerization

Prepolymerizations employing an extremely high stereospecific and high active catalyst based on TiCl₃ modified by di-n-butyl ether (DBE) were carried out with different monomers (styrene, propylene, hexene-1, cyclopentadiene). The influence of prepolymerization on the morphology of polypropylene obtained with TiCl₃ catalyst was investigated. The catalyst was synthesized by TiCl₄ reduction in toluene solution with A1Et₃·DBE complex. The polymer morphology was evaluated through optical and scanning electron microscopies and polymer bulk density and particle size distribution. © 1994 John Wiley & Sons, Inc.     

Kationische Pfropfung von Isobutylen auf chloriertes Polycyclopentadien

Cationic Grafting of Isobutene onto Chlorinated Polycyclopentadiene The effect of reaction conditions on the cationic grafting of isobutene onto chlorinated polycyclopentadiene has been investigated, varying particularly temperature, solvent and coinitiator. The coinitiators used were Et₃Al, Et₂AlCl, Et₃Al₂Cl₃, EtAlCl₂, AlCl₃ and SnCl₄. The solvents used were methylenchloride and dichloroethane. The graft copolymers were characterized by conversion, extraction with n-pentane and GPC. Only Et₃Al₂Cl₃, EtAlCl₂ and AlCl₃ let to a higher grafting efficiency.     

Polymerization of ethylene by zirconocene—B(C6F5)3catalysts with aluminum compounds

Ethylene polymerization by zirconocene—B(C₆F₅)₃ catalysts with various aluminum compounds has been investigated. It is found that the catalytic activity depended on zirconocenes used, and especially on the type of aluminum compounds. For Et(H₄Ind)₂ZrCl₂ (H₄Ind: tetrahydroindenyl), the activity decreases in the following order: Me₃Al > i-Bu₃Al > Et₃Al ≫ Et₂AlCl. While for Cp₂ZrCl₂(Cp : cyclopentadienyl), it varies as follows: i-Bu₃Al > Me₃Al ≫ Et₃Al. Furthermore, the activity is significantly affected by the addition mode of the catalytic components, which may imply that the formation of active centers is associated with an existing concentration of catalytic components. Results of thermal behavior of polyethylene (PE) studied by differential scanning calorimetry (DSC) show that crystallinity of the polymer prepared with Et₃Al is higher than that with Me₃Al or i-Bu₃Al. It is also found that the number-average molecular weight (M ) of the polymers prepared with Me₃Al or i-Bu₃Al is much higher than that with Et₃Al. ¹H-NMR studies substantiate that i-Bu₃Al is a more efficient alkylation agent of Cp₂ZrCl₂ in comparison with Me₃Al. © 1997 John Wiley & Sons, Inc. JAppl Polym Sci 66: 1715–1720, 1997     

Low-pressure polymerization of ethylene. II

This paper presents the kinetic study of polymerization of ethylene with VOCl₃ and aluminum alkyls such as Et₃Al and Et₂AlCl. The effect of various parameters like the [Al]/[V] ratio, catalyst concentration, reaction time, temperature, solvents, and additives on rate of the reaction, yield, and molecular weight is reported. Each of these parameters has a remarkable effect on the yield and the rate of polymerization for both catalyst systems. Triethylamine is found to increase the catalyst efficiency and the rate. It is also observed that aliphatic hydrocarbons acted as a better polymerization medium than did the aromatic ones.     

Novel magnetic polyethylene nanocomposites produced by supported nanometre magnetic Ziegler–Natta catalyst

This paper describes the preparation of novel magnetic polyethylene nanocomposites using a nanometre magnetic Ziegler–Natta catalyst. It was found that novel magnetic polyethylene nanocomposites can be obtained according to the following four steps: (1) preparation of nanometre magnetic particles; (2) reaction between AlR₃ and hydroxyls on the surface of nanometre magnetic particles to form anchor points  AlR₂; (3) addition of TiCl₄, Ti being coordinated to anchor points on the surface of nanometre magnetic particles to form polymerization active centres; (4) ethylene polymerization being carried out in situ on the surface of the nanometre magnetic particles to produce novel magnetic polyethylene nanocomposites. It is found that the activity of ethylene polymerization is essentially unaffected by polymerization temperature and polymerization time. © 2000 Society of Chemical Industry     

Kationische Pfropfung von Butadien auf chloriertes Polycyclopentadien

Cationic Grafting of Butadiene onto Chlorinated Polycyclopentadiene The influence of the reaction conditions on the cationic grafting of butadiene onto chlorinated polycyclopentadiene (CPCPD) has been investigated. Apart from varying the temperature, the solvent and the coinitiator the behaviour of CPCPD resp. butadiene against the used coinitiators triethylaluminium (Et₃Al), diethylaluminium monochloride (Et₂AlCl), ethylaluminium sesquichloride (Et₃Al₂Cl₃) and ethylaluminium dichloride (EtAlCl₂) was studied. The solvents used were chlorbenzene, methylenchloride, dichloroethane and mixtures of them with carbontetrachloride. The graft copolymers were characterized by conversion, grafting efficiency, percentage of grafting, spectroscopic methods, and GPC. The grafting efficiency is only little affected by temperature and type of the coinitiator. With Et₃Al as a coinitiator no graft copolymers are obtained.     

Ethylene polymerization with heterogeneous Ziegler-Natta catalysts

Summary TiCl₄/SiO₂, Ti(OC₄H₉)₄/SiO₂, MgCl₂/TiCl₄/SiO₂ and MgCl₂/Ti(OC₄H₉)₄/SiO₂ catalysts were prepared by treating silica gel with TiCl₄, Ti(OC₄H₉)₄, MgCl₂/TiCl₄ or MgCl₂/Ti(OC₄H₉)₄ in tetrahydrofuran (THF) solution. Ethylene polymerization was performed with these catalysts activated by common alkylaluminum compounds. The influence of magnesium dichloride on catalyst performance was investigated. MgCl₂ has enhanced the catalyst activity for both titanium compounds. In addition, all catalyst systems were only active when they were washed with AlCl(C₂H₅)₂ (DEAC).     

Effect of an external donor upon chain-transfer reactions in propylene polymerization with a MgCl2-supported titanium catalyst system

The chain-end groups of the polypropylene (PP) polymerized without addition of molecular hydrogen over a MgCl₂·TiCl₄·dioctylphthalate/Et₃Al catalyst system consisted of n-butyl, n-propyl, vinylidene and vinyl groups in addition to ethyl and i-butyl groups which were detected in the PP prepared under the same polymerization conditions except for the addition of diphenyldimethoxysilane (DPDMS) as an external donor. The newly detected chain-end groups indicate that the additional chain-transfer reactions were brought about by Et₃Al at 2,1-inserted sites and by β-hydrogen elimination at both 1,2- and 2,1-inserted sites. These chain-transfer reactions could account for the observed drops of the activity and the molecular weight in the absence of DPDMS. In addition, the detected chain ends in the PP polymerized with addition of molecular hydrogen over this catalyst system having no DPDMS suggest that the molecular hydrogen addition leads not only to the conversion of the dormant 2,1-inserted sites into the active sites, but also to a decrease in the frequency of 2,1-insertion.