Kinetic features of ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl₂/MgCl₂‐Al(i‐Bu)₃ (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007     

Ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

Data on ethylene polymerization over supported LFeCl₂/MgCl₂ catalysts {L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl]pyridyl} containing AlR₃ (R = Me, Et, i‐Bu, or n‐Oct) as an activator are presented. These catalysts are highly active (100–300 kg of polyethylene/g of Fe h bar of C₂H₄) and stable in ethylene polymerization at 70–80 °C. Data on the effects of the iron content, AlR₃ type, Al(i‐Bu)₃ concentration, and hydrogen presence on the catalyst activity are presented. The molecular structure of polyethylene produced with these catalysts (including the molecular masses, molecular mass distribution, branching, and number of C?C bonds) has been studied; data on the effects of AlR₃ and hydrogen on the molecular structure are presented. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2128–2133, 2005     

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     

Homogeneous and supported catalysts based on bis(imino)pyridyl Iron(II) complexes for ethylene polymerization

Data on ethylene polymerization on homogeneous and supported catalysts based on 2,6-bis(imino)pyridyl Fe(II) complexes activated by trialkylaluminums are considered (activity, the molecular-weight characteristics of polymers, the number of active sites, and the propagation rate constants). Unlike homogeneous systems, the supported catalysts prepared with the use of various carriers (SiO₂, Al₂O₃, and MgCl₂) exhibited high stability and activity at 70–80°C and produced high-molecular-weight polyethylene with a broad molecular-weight distribution (MWD). The molecular weights and MWDs of polymers and the propagation rate constant depended on the nature of the carrier only slightly. The reasons for an unusual effect of an increase in the activity of the supported catalysts in ethylene polymerization in the presence of hydrogen are discussed.     

MAO‐Free Activation of Metallocenes and other Single‐Site Catalysts for Ethylene Polymerization using Spherical Supports based on MgCl2

Summary: Supports of type MgCl₂/AlR_n(OEt)_3−n, obtained by reaction of AlR₃ with adducts of MgCl₂ and ethanol, have been shown to be effective for the immobilization and activation of [Cp₂TiCl₂] and other single‐site olefin polymerization catalysts without the use of methylaluminoxane or a borate activator. Polyethylene with a spherical particle morphology and narrow molecular weight distribution was obtained.

     

Metallocene–methylaluminoxane catalysts for olefin polymerizations. IV. Active site determinations and limitation of the 14CO radiolabeling technique

The initial active site concentrations, [C^*]₀, have been determined with CH₃OT radiolabeling for the Cp₂ZrCl₂/MAO and CpZrCl₃/MAO catalysts (Cp = η⁵ : cyclopentadienyl, MAO = methyl aluminoxane). Almost all the Zr are found to be catalytically active in 70°C ethylene polymerizations; [C^*]₀ = [Zr] and [C^*]₀ = 0.8[Zr] at Al/Zr ratios of 10⁴ and 10³, respectively. Lowering the temperature to 50°C and Al/Zr to 5.5 × 10² reduces [C^*]₀ to 0.2[Zr]. The rate constant of propagation at 70°C was calculated to be 1.6 × 10³(M s)^?1 for both catalysts at Al/Zr = 1.1 × 10⁴; the values are decreased fivefold and tenfold, respectively, for the CpZrCl₃ and Cp₂ZrCl₂ systems. The usage of ¹⁴CO to determine the propagating Zr–P species was investigated. With regard to the time of reaction of ¹⁴CO with the polymerization mixture, the initial phase is attributed to reversible CO complexation and reversible migratory insertion. The second slower phase may be due to the formation of enediolate. During the course of a batch polymerization the ¹⁴C radioactivity incorporated is small compared to the number of active sites found by CH₃OT determination; it is only ca. 10% of [C^*]₀ at maximum rate of polymerization. Therefore, ¹⁴CO radiolabeling cannot be used to count C^*.     

Syndiotactic 1,2-polybutadiene with Co-CS2 catalyst system. III. 1H- and 13C-NMR study of highly syndiotactic 1,2-polybutadiene

The ¹H and ¹³C-NMR spectra of highly crystalline syndiotactic 1,2-polybutadiene (s-PB) are discussed in order to clarify the mechanism of butadiene polymerization with cobalt compound–organoaluminum–CS₂ catalysts. Cis opening of the double bonds in the syndiotactic polymerization is affirmed by the study of the copolymer from perdeuteriobutadiene and cis,cis-1,4-dideuteriobutadiene. S-PB (mp 210°C) has 99.7% 1,2 units, 0.3% isolated cis-1,4 units, and 99.6% syndiotacticity. Polymer ends (2-methyl-3-butenyl group and conjugated diene structure) are also determined. The differences in free energy of activation between 1,2 and cis-1,4 propagation and between syndiotactic and isotactic propagation are 14.0 and 9.6 kcal/mol, respectively, for Co(acac)₃-AlEt₃-AlEt₂Cl-CS₂, and 6.7 and 5.7 kcal/mol, respectively, for the aluminum-free Co(C₄H₆)(C₈H₁₃)CS₂ system. The conformation of s-PB in o-dichlorobenzene at 150°C is described by the sequence (tt)_1.6(gg)(tt).     

Kinetic regularities of catalytic ethylene polymerization on single- and multi-site cobalt and vanadium bis(imino)pyridine complexes

The number of active centers C _p in the homogeneous complexes LCoCl₂ and LVCl₃ (L = 2,6-(2,6-R₂C₆H₃N=CMe)₂C₅H₃N; R = Me, Et, ^t Bu) and the propagation rate constants k _p have been determined by the radioactive ¹⁴CO quenching of ethylene polymerization on these complexes in the presence of the methylaluminoxane (MAO) activator. For the systems studied, a significant portion of the initial complex (up to 70%) transforms into polymerization-active centers. The catalysts based on the cobalt complexes are single-site, and the constant k _p in these systems is independent of the volume of substituent R in the ligand, being (2.4?3.5) × 10³ L mol^?1 s^?1 at 35°C. The much larger molecular weight of the polymer formed on the complex with the tert-butyl substituent in the aryl rings of the ligand compared to the product formed on the complex with the methyl substituent is due to the substantial (～11-fold) decrease in the rate constant of chain transfer to the monomer. At the early stages of the reaction (before 5 min), the vanadium complexes contain active centers of one type only, for which k _p = 2.6 × 10³ L mol^?1 s^?1 at 35°C. An increase in the polymerization time to 20 min results in the appearance, in the vanadium systems, of new, substantially less reactive centers on which high-molecular-weight polyethylene forms. The number of active centers C _p in the 2,5-tBu₂LCoCl₂ and 2,6-Et₂LVCl₃ systems with the MAO activator increases as the polymerization temperature is raised from 25 to 60°C. The activation energies of the chain propagation reaction (E _p) have been calculated. The value of E _p for complex 2,5-tBu₂LCoCl₂ is 4.5 kcal/mol. It is assumed that the so-called “dormant” centers form in ethylene polymerization on the 2,6-Et₂LVCl₃ complex, and their proportion increases with a decrease in the polymerization temperature. Probably, the anomalously high value E _p = 14.2 kcal/mol for the vanadium system is explained by the formation of these “dormant” centers.     

Styrene polymerization with nickel complexes/methylaluminoxane catalytic system

Polymerization of styrene using β‐diketiminate nickel (II) bromide complexes CH{C(R)NAr}₂NiBr (R = CH₃, Ar = 2,6‐ⁱPr₂C₆H₃, 1 ; R = CH₃, Ar = 2,6‐Me₂C₆H₃, 2 ; R = CF₃, Ar = 2,6‐ⁱPr₂C₆H₃, 3 ; R = CF₃, Ar = 2,6‐Me₂C₆H₃, 4 ) in the presence of methylaluminoxane was studied. Compound 3 is the most active styrene polymerization catalyst of all the nickel complexes tested. The activity of these catalysts increases with increases in steric bulk of the substituents on the aryl rings. The electronic nature of the ligand backbone also affects the activity. Weight‐average molecular weight of the prepared polystyrene ranges from 21 000 to 72 000, with polydispersity indexes of 1.95–2.78. The microstructure of the obtained products is atactic polystyrenes from NMR analyses. Copyright © 2008 John Wiley & Sons, Ltd.     

Polymerization of methyl methacrylate using a metallocene catalyst system

Methyl methacrylate was polymerized with Cp₂YCl(THF) or IVB group metallocene compounds (i.e., Cp₂ZrCl₂ and Cp₂HfCl₂, etc.), in the presence of a Lewis acid like Zn(C₂H₅)₂. The Lewis acid was complexed with methyl methacrylate, which avoided the metallocene compounds being poisoned with a functional group. A living polymerization was promoted through the use of metallocene/MAO/Zn(C₂H₅)₂, which gave tactic poly(methyl methacrylate) with a high molecular weight. The polymer yield increases with polymerization time, which indicates that the propagation rate is zero in order in the concentration of the monomer. The polymer yield increases also with the concentration of Cp₂YCl(THF), which indicates the yttrocene to be the real catalyst. When the polymerization temperature exceeds room temperature, the poly(methyl methacrylate) cannot be synthesized by the Cp₂YCl(THF) catalyst. When the reaction temperature reachs −60 °C, the poly(methyl methacrylate) is high syndiotatic and molecular weight by the Cp₂YCl(THF)/MAO catalyst system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1184–1194, 2000     

Quantum Chemical Investigation of the Initial Steps of the Yttrium‐Mediated Polymerization of Ethene and Propene

The mechanistic details of the initial steps of the polymerization brought about by a dicyclopentadienyl yttriumhydrid catalyst have been computationally investigated using approximate density functional theory. In accord with the experimental information, the overall reaction sequence Cp₂YH + C₂H₄ → Cp₂Y–C₂H₅ and Cp₂YH + C₃H₆ → Cp₂Y–C₃H₇ is computed to be exothermic by ca. 22.2 and 20.8 kcal mol^–1, respectively. The reaction mechanism predicted by our calculations is in harmony with the available experimental information but provides additional information into the various elementary steps of this reaction, which could not be obtained by experimental means.     

Copolymerization of ethylene and 1-hexene with TiCl4/MgCl2 catalysts modified by 2,6-diisopropylphenol

A supported TiCl4/MgCl2 catalyst without internal electron donor (O-cat) was prepared firstly. Then it was modified by 2,6-diisopropylphenol to make a novel modified catalyst (M-cat). These two catalysts were used to catalyze ethylene/1-hexene copolymerization and 1-hexene homopolymerization. The influence of cocatalyst and hydrogen on the catalytic behavior of these two catalysts was investigated. In ethylene/1-hexene copolymerization, the introduction of 2,6-iPr2C6H3O-groups did not deactivate the supported TiCl4/MgCl2 catalyst. Although the 1-hexene incorporation in ethylene/1-hexene copolymer prepared by M-cat was lower than that prepared by O-cat, the composition distribution of the former was narrower than that of the latter. Methylaluminoxane (MAO) was a more effective activator for M-cat than triisobutyl-aluminium (TIBA). MAO led to higher yield and more uniform chain structure. In 1-hexene homopolymerization, the presence of 2,6-iPr2C6H3O-groups lowered the propagation rate constants. Two types of active centers with a chemically bonded 2,6-iPr2C6H3O-group were proposed to explain the observed phenomena in M-cat.     

Propylene polymerization with catalysts containing divalent titanium

The behavior in propylene polymerization of divalent titanium compounds of type [η⁶-areneTiAl₂Cl₈], both as such and supported on activated MgCl₂, has been studied and compared to that of the simple catalyst MgCl₂/TiCl₄. Triethylaluminium was used as cocatalyst. The Ti–arene complexes were active both in the presence and in the absence of hydrogen, in contrast to earlier reports that divalent titanium species are active for ethylene but not for propylene polymerization. ¹³C-NMR analysis of low molecular weight polymer fractions indicated that the hydrogen activation effect observed for the MgCl₂-supported catalysts should be ascribed to reactivation of 2,1-inserted (“dormant”) sites via chain transfer, rather than to (re)generation of active trivalent Ti via oxidative addition of hydrogen to divalent species. Decay in activity during polymerization was observed with both catalysts, indicating that for MgCl₂/TiCl₄ catalysts decay is not necessarily due to overreduction of Ti to the divalent state during polymerization. In ethylene polymerization both catalysts exhibited an acceleration rather than a decay profile. It is suggested that the observed decay in activity during propylene polymerization may be due to the formation of clustered species that are too hindered for propylene but that allow ethylene polymerization. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2645–2652, 1997     

Micron‐granula polyolefin with self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups

Self‐immobilized nickel and iron diimine catalysts bearing one or two allyl groups of [ArN?C]₂(C₁₀H₆)NiBr₂ [Ar = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₂] ( 1 ), [ArN?C(Me)][Ar′N? C(Me)]C₅H₃NFeCl₂ [Ar = Ar′ = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₃, Ar = 2,6‐(i‐Pr)₂C₆H₃, and Ar′ = 4‐allyl‐2,6‐(i‐Pr)₂C₆H₃] were synthesized and characterized. All three catalysts were investigated for olefin polymerization. As a result, these catalysts not only showed high activities as the catalyst free from the allyl group, such as [ArN?C]₂C₁₀H₆NiBr₂ (Ar = 2,6‐(i‐Pr)₂C₆H₂)], but also greatly improved the morphology of polymer particles to afford micron‐granula polyolefin. The self‐immobilization of catalysts, the formation mechanism of microspherical polymer, and the influence on the size of the particles are discussed. The molecular structure of self‐immobilized nickel catalyst 1 was also characterized by crystallographic analysis. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1018–1024, 2004     

Synthesis and polymerization behavior of novel C 1 and C s titanium ansa‐cyclopentadienyl‐amido catalysts for ethylene and propylene polymerization

Four titanium ansa‐cyclopentadienyl‐amido complexes of the general formula [C₅H₃RMe₂SiN(2,6‐Me₂C₆H₃)]TiX₂(R = H,Me,Bz,^tBu;X = NMe₂ or Cl) have been synthesized. The complexes polymerize both ethylene and propylene in the presence of methylaluminoxane or Ph₃CB(C₆F₅)₄–triisobutylaluminum and were most active at lower temperatures. In general, the smaller the substituent on the cyclopentadienyl group, the more active the catalyst. The catalysts were found to be poorly stereoselective for the polymerization of polypropylene, with the tertiary‐butyl substituted catalyst giving a polymer with the greatest [mmmm] (14.2%). The structure of [C₅H₄Me₂SiN(2,6‐Me₂C₆H₃)] Ti(NMe₂)₂ was determined by X‐ray diffraction. The complex crystallizes in the monoclinic system space group P2₁/n, with a = 16.437(2), b = 8.652(3), c = 16.494(4),β = 117.54(2) and Z = 4. Copyright © 2002 John Wiley & Sons, Ltd.     

Development of novel MgCl2 supported catalyst with trivalent titanocene complex of CP2TiCl2AlCl2 for propylene polymerization

Three kinds of MgCl₂‐supported trivalent titanocene catalyst (Cat. 1: Cp₂TiCl₂AlCl₂/MgCl₂, Cat. 2: CpCp*TiCl/MgCl₂, Cat. 3: Cp₂TiCl/MgCl₂) were prepared and tested for propylene polymerization. It was found that Cat. 1, combined with ordinary alkylaluminum as cocatalyst, produced PP containing 31.8 wt % of isotactic PP in fairly good yield. On the other hand, Cats. 2 and 3 hardly showed any activity. The effects of diisopropyldimethoxysilane (DIPDMS) on isospecificity of the Cat. 1 also were investigated. The isotactic index (I.I.) of PP was improved drastically by the addition of DIPDMS as external donor and reached the value as high as 98.4%, even in the absence of any internal donors. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3355–3359, 2000     

Stereospecific styrene polymerization and ethylene–styrene copolymerization with titanocenes containing a pendant amine donor

A series of monocyclopentadienyl titanium complexes containing a pendant amine donor on a Cp group ( A = CpTiCl₃, B = Cp^NTiCl₃, C = Cp^NTiCl₂TEMPO, for Cp = C₅H₅, Cp^N = C₅H₄CH₂CH₂N(CH₃)₂, and TEMPO = 2,2,6,6‐tetramethylpiperidine‐N‐oxyl) are investigated for styrene homopolymerization and ethylene–styrene (ES) copolymerization. When activated by methylaluminoxane at 70 °C, complexes with the amine group ( B and C ) are active for styrene homopolymerization and afford syndiotactic polystyrene (sPS). The copolymerizations of ethylene and styrene with B and C yield high‐molecular weight ES copolymer, whereas complex A yields mixtures of sPS and polyethylene, revealing the critical role that the pendant amine has on the polymerization behavior of the complexes. Fractionation, NMR, and DSC analyses of the ES copolymers generated from B and C suggest that they contain sPS. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1579–1585, 2010     

Kinetics of hexene‐1 polymerization using [(N,N′‐diisopropylbenzene)‐2,3‐(1,8‐napthyl)‐1,4‐diazabutadiene] dibromonickel/methylaluminoxane catalyst system

Kinetics of hexene‐1 polymerization was investigated using [(N,N′‐diisopropylbenzene)2,3‐(1,8‐napthly)‐1,4‐diazabutadiene]dibromonickel/methylaluminoxane catalyst. Experiments were performed at varying catalyst and monomer concentrations in the temperature range of ?10 to 35 °C. First order time‐conversion plot shows a downward curvature at temperatures of 20 °C and 35 °C indicating the presence of finite termination reactions. A nonlinear plot of degree of polymerization (P_n) with respect to conversion indicates occurrence of transfer reactions and slow initiation. The experimental molar masses are higher than predicted, which implies that a fraction of catalyst species could not be activated or is deactivated at the early stages of the reactions. The efficiency of the catalyst (Cat_eff) varies from 0.77 to 0.89. The observed polydispersity of the poly(hexene‐1) s is in the range of 1.18–1.48. The reaction order was found to be 1.11 with respect to catalyst. The Arrhenius plot obtained using the overall propagation rate constant, k_p, at five different temperatures (?10, 0, 10, 20, and 35 °C) was found to be linear with an activation energy, E_a = 4.3 kcal/mol. Based on the results presented it is concluded that the polymerization of hexene‐1 under the above‐mentioned conditions shows significant deviation from ideal “living” behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1093–1100, 2007     

Superactive and stereospecific catalysts. I. Structures and productivity

Two series of catalysts were made, one from MgCl₂–A solution containing MgCl₂, EH (2-ethylhexanol), and EB (ethyl benzoate) dissolved in decane and another from MgCl₂–B solution containing MgCl₂, EH, and phthalic anhydride which reacted to form the corresponding phthalic ester. Reactions of these solutions with TiCl₄ with or without another ester produced a family of eight catalysts. They form two groups, one having monoesters as modifiers, and the other containing diesters as modifiers. The surface area, pore volume, x-diffractions, polymerization activity, and catalytic stereospecificity of these catalysts have been compared. The diester catalysts differ from the monoester catalysts in every respect. By comparison the corresponding member of the diester catalysts have half as much Ti per Mg, more than 10 times the pore volume, more than a 100-fold the surface area, about 50% more productivity, and greatly increased steroespecificity.     

Kinetic study of ethylene polymerization with chromium oxide catalysts by a radiotracer technique

The quenching of polymerization with a chromium oxide catalyst by radioactive methanol ¹⁴CH₃OH enables one to determine the concentration of propagation centers and then to calculate the rate constant of the propagation. The dependence of the concentration of propagation centers and the polymerization rate on reaction time, ethylene concentration, and temperature was investigated. The change of the concentration of propagation centers with the duration of polymerization was found to be responsible for the time dependence of the overall polymerization rate. The propagation reaction is of first order on ethylene concentration in the pressure range 2–25 kg/cm². For catalysts of different composition, the temperature dependence of the overall polymerization rate and the propagation rate constant were determined, and the overall activation energy E_ov and activation energy of the propagation state E_p were calculated. The difference between E_ov and E_p is due to the change of the number of propagation centers with temperature. The variation of catalyst composition and preliminary reduction of the catalyst influence the shape of the temperature dependence of the propagation center concentration and change E_ov.