Presence Of Methylaluminoxane Research Articles

Functional surface groups for single-site heterogeneous α-olefin polymerization catalysts

A novel heterogeneous α-olefin polymerization catalyst is prepared by the immobilization of CpZrCl 3 on a chemically modified silica support. The surface modification of silica was carried out by utilizing the saturated gas-solid reactions of a silane coupling agent with a hydrocarbon spacer, Cp(CH 2) 3Si(OCH 2CH 3) 3, and a partially dehydroxylated silica. In gas-solid reactions all reactive surface hydroxyl groups were utilized in bonding the silane coupling agent on silica. The immobilization of CpZrCl 3 on the cyclopentadienyl surface formed on the silica was done using liquid-phase reactions. The prepared materials were characterized by FT-IR spectroscopy. The supported catalyst system has a high activity in ethylene polymerization and can be used to produce polyethylene with a narrow molecular weight distribution in the presence of methylaluminoxane. The catalytic activity was doubled when CpZrCl 3 was immobilized on the cyclopentadienyl surface of SiO 2 compared with the activity of CpZrCl 3 in homogeneous catalysis. However, the direct heterogenization of CpZrCl 3 onto unmodified silica produced a catalyst with a very low activity. The effect of surface modification reactions and the surface structure of a support on the catalyst performance is presented and discussed.

Ethylene polymerizations with disiloxane‐bridged indenyl and cyclopentadienyl metallocene catalysts

Abstractansa‐Tetramethyldisiloxane‐bridged indenyl, tetrahydroindenyl and cyclopentadienyl zirconium complexes 1–4 were prepared. The pure rac‐1–3 and meso‐1–2 complexes were separated by fractional crystallization. Indenyl complexes, both rac‐1 and meso‐1, in the presence of methylaluminoxane (MAO), have very high activities for ethylene polymerization. The molecular weight of polyethylene produced with rac‐1 is extremely high and significantly dependent on polymerization temperature. The tert‐butyl‐substituted cyclopentadienyl complex exhibits low activity and produces polyethylene of low molecular weight.

Cyclopentadienyl Surface as a Support for Zirconium Polyethylene Catalysts

A novel ethylene polymerization catalyst is prepared by supporting CpZrCl3 on chemically modified silica. The surface modification of silica was carried out by utilizing the saturated gas−solid reactions of a silane coupling agent, Cp(CH2)3Si(OCH2CH3)3, and a partially dehydroxylated silica. Immobilization of CpZrCl3 onto the cyclopentadienyl surface formed on the silica was done using liquid-phase reactions. The stepwise-prepared materials were characterized by 13C and 29Si solid state NMR and FT-IR spectroscopy. This supported catalyst system has a high activity and can be used to produce polyethylene with a narrow molecular weight distribution in the presence of methylaluminoxane. The immobilization of CpZrCl3 on the cyclopentadienyl surface of SiO2 more than doubled the polymerization activity of CpZrCl3. However, the direct heterogenization of CpZrCl3 onto an unmodified, partially dehydroxylated silica produced a catalyst with a very low activity. The effect of surface modification reactions and structure of the support on the catalyst performance is presented and discussed.

Synthesis, structure, and catalytic properties of ansa-Zirconocenes, Me 2X(Cp)(RInd) ZrCl 2 (X = C, Si; R = 2- p- or 3- p-tolyl)

ansa-Zirconocenes, Me 2X(Cp)(3-Tollnd)ZrCl 2 [X = C ( 7), Si ( 8); Cp = η 5-C 5H 5; Tol = p-C 6H 4CH 3] and Me 2Si(Cp)(2-TolInd)ZrCl 2 ( 9), have been prepared by the reactions of ZrCl 4 with the corresponding dilithiated ligands in diethyl ether at −78°C. The molecular structure of complex 9 has been determined by a single crystal X-ray diffraction study. Propylene polymerization has been studied for complexes 7, 8 and 9 in the presence of methylaluminoxane (MAO). Complex 9 reveals the highest catalytic activity of 1570kg PP/(mol Zr h atm) and the highest molecular weight of 1.2 × 10 6 among the three catalysts. Complex 9 produces atactic polypropylene (PP), whereas 7 and 8 afford PP with a weak syndiotacticity at low temperature.

Copolymerization of ethylene and 1,5-hexadiene under high pressure catalyzed by a metallocene

The copolymerization of ethylene and 1,5-hexadiene was investigated under high pressure of 1500 bar using a zirconocene catalyst in the presence of methylaluminoxane. The concentration of the diene was varied over a wide range including the homopolymerization of both ethylene and 1,5-hexadiene. From the amount of polymer formed per unit of time and the catalyst feed the productivity was determined. The resulting polymers were analyzed by DSC, GPC, IR- and 13 C -NMR-spectroscopy to evaluate the average molecular weights together with the polydispersity, the crystallinity, the melting point and the structure. The catalyst exhibits a good ability for copolymerization and cyclopolymerization of 1,5-hexadiene in which a predominance of trans ring formation was observed.

Magnesium chloride supported bis(cyclopentadienyl)titanium(IV) dichloride‐MAO catalyst for ethylene polymerization

AbstractA novel magnesium chloride supported titanocene catalyst was synthesized using a soluble tetrahydrofuran complex of magnesium chloride. The suported catalyst polymerized ethylene with high activities in presence of methylaluminoxane. The significant feature of the supported metallocene catalyst is that it shows high polymerization activity at low Al/Ti ratio and at higher temperatures compared to soluble catalyst. The role of support in stabilizing the active species on the metallocene is discussed.

Synthesis and polymerization behavior of various substituted indenyl titanium complexes as catalysts for syndiotactic polystyrene

Five substituted indenyltrichlorotitanium compounds have been synthesized and characterized by spectroscopic methods and their catalytic behavior for the polymerization of styrene was studied in the presence of methylaluminoxane (MAO) as a cocatalyst. Substituted indenyl ligands include 1,3-dimethyl, 1-methyl, 1-ethyl, 1-isopropyl and 1-(trimethylsilyl)indenyl groups. All five compounds gave extremely pure syndiotactic polystyrene, with conversion rates of at least 95%, and their catalytic properties were compared with the data obtained from the ( η 5-indenyl)trichlorotitanium-MAO system. The catalytic activity is enhanced by less bulky and better electron-releasing substituents of the indenyl ligand.

Synthesis, characterization, and reactivities of the polysiloxane-bridged binuclear metallocenes tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride) and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride)

The reaction of dithallium salts of tetramethyldisiloxanediylbis(cyclopentadienyl), 3, and hexamethyltrisiloxanediylbis(cyclopentadienyl), 4, with two equivalents of TiCl 4 gives the title compounds tetramethyldisiloxanediylbis(cyclopentadienyltitanium trichloride), 5 and hexamethyltrisiloxanediylbis(cyclopentadienyltitanium trichloride), 6 respectively. The stoichiometric reaction of 5 and 6 with water results in the formation of new oxygen-bridged metallocenes [(TiCl 2) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 2O], 7, and [(TiCl 2) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 3O 2}], 8. In addition, further reaction of 7 and 8 with another one equivalent of water or the treatment of 5 and 6 with an excess amount of water gives rise to the formation of the metallocene compounds having Ti 4O 4 rings [(TiCl) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 2O] 2( μ 2-O) 2, 9, and [(TiCl) 2( μ 2-O)-( η 5-C 5H 4) 2- μ 2-(SiMe 2) 3O 2] 2 ( μ 2-O) 2, 10. All the new kinds of metalocenes prepared have been characterized by IR, NMR, mass spectrometry, or elemental analysis. Especially an investigation of the Δδ values in 1H NMR and a comparison between the theoretical and observed isotopic ratio in a mass spectra among the synthesized bridged compounds have been very conveniently utilized to study their structures. Polymerization experiments with the dinuclear complexes in the presence of methylaluminoxane as a cocatalyst indicate that the compounds 5 and 6 do exhibit catalytic activity for syndiotactic polymerization of styrene.

Enzymatic and Environmental Degradation of Racemic Poly(3-hydroxybutyric acid)s with Different Stereoregularities

Racemic poly(3-hydroxybutyric acid) (P(3HB)) was prepared by the ring-opening polymerization of racemic β-butyrolactone (β-BL) in the presence of methylaluminoxane and fractionated into five components with various isotactic diad fractions ([i]) varying from 0.88 to 0.54. The degree of X-ray crystallinity of isotactic P(3HB) films decreased from 33 to 8% as the [i] value was decreased from 0.88 to 0.54. A predominantly syndiotactic P(3HB) ([i] = 0.30) was prepared by the polymerization of racemic β-BL in the presence of 1-ethoxy-3-chlorotetrabutyldistannoxane, and its crystallinity was 26%. Enzymatic degradation of P(3HB) films with different stereoregularities was carried out at 37 °C in 0.1 M potassium phosphate buffer (pH 7.4) in the presence of PHB depolymerase purified from Alcaligenes faecalis. The highest rate of enzymatic hydrolysis was observed at an [i] value of 0.74. Syndiotactic P(3HB) film was hardly hydrolyzed by the enzyme. The enzymatic degradation products of racemic P(3HB) samples ([i] =...

Ethylene and Propylene Polymerization over Chiral ansa-Dichloro[o-phenylenedimethylenebis(.eta.5-1-indenyl)]zirconium [Zr{C6H4(CH2-1-C9H6)2-1,2}Cl2

ansa-Dichloro[o-phenylenedimethylenebis( n 5 -1-indenyl)]zirconium (1) has been prepared from the reaction of dilithiated bis(1-indenyl)-o-xylene with ZrCl 4 in tetrahydrofuran. A rac-1/meso-I ratio close to 1 is obtained, and the diastereomeric complexes have been separated by fractional crystallization. Polymerizations of both ethylene and propylene with rac-1 and meso-1 in the presence of methylaluminoxane (MAO) as cocatalyst have been examined. In ethylene polymerization, mesa-1 is more active than rac-1, while in propylene polymerization, the latter is much more active than the former. The polymerization data and the stereochemical analysis of the obtained polypropylene (PP) by 13 C NMR spectroscopy reveal that both the activity of the rac-1/MAO catalyst and the stereoregularity of PP are low due to the distortion of catalyst rac-1 from the C 2 symmetry and the fluxionality of the ansa-ligand, which is caused by the four carbon atoms of the rigid o-phenylenedimethylene bridge.

Living Polymerization of Ethylene Catalyzed by Diene Complexes of Niobium and Tantalum, M(.eta.5-C5Me5)(.eta.4-diene)X2 and M(.eta.5-C5Me5)(.eta.4-diene)2 (M = Nb and Ta), in the Presence of Methylaluminoxane

Living Polymerization of Ethylene Catalyzed by Diene Complexes of Niobium and Tantalum, M(.eta.5-C5Me5)(.eta.4-diene)X2 and M(.eta.5-C5Me5)(.eta.4-diene)2 (M = Nb and Ta), in the Presence of Methylaluminoxane

Elastomeric Poly(propylene): Influence of Catalyst Structure and Polymerization Conditions on Polymer Structure and Properties

A number of propylidene- and dimethylsilylene-bridged metallocene complexes of titanium, zirconium, and hafnium were prepared and employed in a study of propylene polymerization in the presence of methylaluminoxane. This work has revealed that catalysts based on hafnium are desirable for the production of elastomeric poly(propylene) in that they polymerize propylene to high molecular weight polymer and are indefinitely stable under typical polymerization conditions. Two of the zirconium complexes prepared have been characterized by X-ray crystallography. [2-Propylidene(η 5 -indenyl)(η 5 -cyclopentadienyl)]zirconium dichloride 3: Space group Pna2 1 ; a=9.792 (2), b=12.156 (3), c=12.751 (3) A; V=1517.8 (5) A 3 ; Z=4; R=0.0176, R w =0.0196 for 2188 reflections with F>6.0(F). [Dimethylsilylene(η 5 -indenyl)(η 5 -cyclopentadienyl)]zirconium dichloride 5: Space group Pbca; a=13.174 (4), b=15.873 (5), c=15.353 (4) A; V=3210.6 (15) A 3 ; Z= 8; R= 0.0351, R w =0.0349 for 2538 reflections with F>6.0(F). The microstructure of the poly(propylene) produced was sensitive not only to changes in catalyst structure but also to polymerization conditions such as temperature. The stereoregularity of the polymer was surprisingly sensitive to changes in monomer concentration (i.e., pressure). By varying both catalyst structure and polymerization conditions, it is possible to produce elastomeric poly(propylene) that exhibits excellent elastic properties

New ansa-metallocenes of the Group 4 transition metals as homogeneous catalysts for the polymerization of propene and styrene

The ansa-bridged metallocenes [M{CR2(η-C5H4)(η-C9H6)}Cl2], [M = Ti, Zr or Hf; CR2= CMe2, CPh2 or C(CH2)5] have been prepared. The crystal structure of [Zr{CMe2(η-C5H4)(η-C9H6)}Cl2] has been determined. Some of these new ansa-metallocenes in the presence of methylaluminoxane (AlMeO)n give homogeneous catalysts, which for the polymerization of propene yield isotactic rich polypropene and of styrene yield syndiotactic polystyrene.

High pressure polymerization of ethylene with a homogeneous metallocene catalyst

AbstractSoluble metallocene catalysts can be easily metered into high pressure polymerization reactors. The performance of a homogeneous zirconocene catalyst for the polymerization of ethylene under high pressures was tested at 1500 bar and temperatures between 80 and 260°C in the presence of methyl aluminoxane as cocatalyst. Besides the productivity of the catalyst and the overall rate of polymerization, the most important properties of the prepared polymers were determined. The results were compared with those found earlier with a heterogeneous titanium catalyst supported on magnesium dichloride.

Polymerization of propylene using supported, chiral, ansa-metallocene catalysts: production of polypropylene with narrow molecular weight distributions

Chiral ansa-metallocenes 1,2-ethylenebis(η 5 -1-indenyl)- and 1,2-ethylenebis(η 5 -1-tetrahydroindenyl)zirconium dichloride can be supported on partially dehydroxylated SiO 2 and AlO 2 and these systems can be used to polymerize propylene in the presence of methylaluminoxane. The most active supported systems were derived from dehydroxylated SiO 2 and AlO 2 that had been treated with excess AlMe 3 . The properties of the polypropylene produced are essentially undistinguishable from that produced under homogeneous conditions with the same catalysts

Homogeneous Ziegler–Natta catalysis. II. Ethylene polymerization by IVB transition metal complexes/methyl aluminoxane catalyst systems

AbstractHomogeneous Ziegler‐Natta systems for the ethylene polymerization, deriving from R2R2′M complexes (R = cyclopentadienyl; R′ = alkyl, aryl; M = Ti, Zr, Hf) and oligomeric oxoalane compounds, were studied. Further results concerning the methyl aluminoxane synthesis and the related chemistry are reported. On the basis of spectroscopic data a delocalized electronic structure could be inferred for these compounds. Results from polymerization experiments showed that the highest productivities are obtained only by oxoalane cocatalysts having a high degree of oligomerization. The catalytic activity of the systems under investigation was strongly affected also by changing both the σ‐alkyl and the π‐cyclo‐pentadienyl ligands. Furthermore, it was found that in the presence of methyl aluminoxane, the homoleptic σ‐alkyl derivatives of IVB transition metals, such as Zr(CH2C6H5)4, are also able to polymerize ethylene with a fairly high productivity. Active species containing ZrOAl bonds have been postulated.