Catalytic Ethylene Polymerization Research Articles

Transition Metal Complexes of Allylated α-Diimines as Self-Immobilizing Catalysts for the Polymerization of Ethylene

A series of allylated α-diimine complexes of Ti, Zr, V, Cr, Fe, Ni, and Pd was prepared and characterized. These complexes were activated with methylaluminoxane (MAO) and tested for catalytic ethylene polymerization. The allyl groups of the ligands can self-immobilize the catalysts and prevent reactor fouling. The catalyst activities and the properties of the obtained polyethylenes are influenced by the metal center and the structure of the corresponding catalyst. The allylated α-diimine nickel catalysts showed the highest activities in the series and produced polyethylenes with higher molecular weights compared to the analogous catalysts without allyl groups. The allylated α-diimine palladium catalysts showed no activities for ethylene polymerization.

Silica Nanofoam (NF) Supported Single- and Dual-Site Catalysts for Ethylene Polymerization with Morphology Control and Tailored Bimodal Molar Mass Distributions

Highly active single- and dual-site catalysts supported on silica nanofoams (NF) enable the control of both polyethylene (PE) morphology and tailoring of bimodal PE molar mass distribution in catalytic ethylene polymerization. In a templating process, aqueous polystyrene (PS) nano suspensions are mineralized and calcinated at 600 °C, thus producing NF with specific surface area of 1200 m2/g and average pore diameter varying between 20 and 80 nm. Mineralization of the aqueous PS nano suspensions in a water-in-oil emulsion affords spherical NF with average diameter of 40 μm and control of pore size. The methylalumoxane- (MAO-) tethered NF immobilizes single-site catalysts such as metallocene (nBuZr), bisiminopyridine iron(II) (Fe) and constrained geometry chinolyl cyclopentadienyl chromium(III) complexes (Cr-1). Immobilization of binary blends of Fe/Cr-1 and nBuZr/Cr-1 affords NF-supported dual-site catalysts. The catalyst activity, PE particle size and molecular weight distribution varies as a function of the NF pore size. Typically, macroporous NF (pore size of 75 nm) are effective supports for Cr-1, producing ultrahigh molecular weight polyethylene (UHMWPE, Mw > 106 g/mol). Dual -site catalysts such as nBuZr/Cr-1 on mesoporous NF (pore size of 20 nm) enable tailoring of bimodal PE molar mass distribution with UHMWPE content increasing with increasing Cr-1/nBuZr molar ratio.

Retraction of “Bimetallic Effects for Enhanced Polar Comonomer Enchainment Selectivity in Catalytic Ethylene Polymerization”

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionNEXTORIGINAL ARTICLEThis notice is a correctionRetraction of “Bimetallic Effects for Enhanced Polar Comonomer Enchainment Selectivity in Catalytic Ethylene Polymerization”Brandon A. Rodriguez, Massimiliano Delferro, and Tobin J. Marks*Cite this: J. Am. Chem. Soc. 2013, 135, 46, 17651Publication Date (Web):November 5, 2013Publication History Published online5 November 2013Published inissue 20 November 2013https://doi.org/10.1021/ja409590rCopyright © 2013 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views2827Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (124 KB) Get e-Alerts Get e-Alerts

Metallocene Catalyzed Ethylene Polymerization with Specially Designed Catalyst Supports and Reaction Systems

SummaryIn heterogeneously catalyzed polymerization of α‐olefins, the characteristics of a solid support material impact the catalyst activity, polymer particle morphology, and resulting polymer properties. Silica is the most widely used support for metallocene catalysts in α‐olefin polymerization processes because of its large surface area and favorable surface properties for catalyst anchoring. Understanding the kinetics of heterogeneous olefin polymerization over a solid‐supported catalyst is often quite complicated because of mass transfer effects and catalyst particle fragmentation during the polymerization. Incomplete or premature fragmentation of support material results in a large fraction of catalyst sites left unavailable for the polymerization, causing some inconsistencies in the performance of the catalyst. Silica‐supported metallocene catalysts for α‐olefin polymerization are known to follow the layer‐by‐layer fragmentation mechanism where the fracture of the silica/polymer layer begins from the surface region of a silica particle and it gradually continues into the center of the particle as fragmentation is complete. In this paper, we present new experimental results on ethylene polymerization with rac‐Et(indenyl)2ZrCl2/MAO catalyst using different types of silica supports to quantitatively assess the effects of support geometry on intrinsic catalytic activity. Flat surface silica, nano‐sized spherical silica, straight cylindrical pore silica, and conventional silica are used as supports. The presence or absence of intraparticle monomer diffusion resistance and particle fragmentation has been shown to have significant effects on the catalytic activity.

Monometallic nickel(II) complexes containing N,N′-iminopyridine chelating ligands with dendritic substituents: The influence of dendrimer topology on the catalytic oligomerization and polymerization of ethylene

Iminopyridine ligands of general formula Gn-PBE-ONN (Gn-PBE=Fréchet-type dendritic wedges of generation G0 (1), G1 (2), G2 (3), and G3 (4); –ONN=-O-4-(2,5-Me2C6H2)-NCH-2-py) have been prepared starting from H-ONN. Reaction of these bidentate ligands with [NiBr2(DME)] results in the nickel(II) complexes [NiBr2(Gn-PBE-ONN)] (5–8). The methylaluminoxane (MAO)-activated monometallic complexes have been studied in the transformation of ethylene into mixtures of polyethylene and oily oligomers, and their catalytic performance scrutinized as a function of dendritic size. A comparison with the behavior observed for related polymetallic dendrimers has enabled the dendritic features that affect various catalytic parameters to be determined. Thus, it has been possible to discern whether the dendritic effect detected in the catalysis should be ascribed to the metallic nuclearity rather than the bulkiness of the metallodendrimer.

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

The number of active centers Cp in the homogeneous complexes LCoCl2 and LVCl3 (L = 2,6-(2,6-R2C6H3N=CMe)2C5H3N; R = Me, Et, tBu) and the propagation rate constants kp 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 kp 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 kp = 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 Cp 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 (Ep) have been calculated. The value of Ep 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 Ep = 14.2 kcal/mol for the vanadium system is explained by the formation of these “dormant” centers.

Titanium (IV) and zirconium (IV) chloride complexes on the base of chiral tetraaryl-1,3-dioxolane-4,5-dimetanol ligands in the polymerization of ethylene: The promoting role of lithium and magnesium chloride

Coordination compounds of titanium (IV) and zirconium (IV) with tetra-aryl-1,3-dioxolan-4,5-dimethanol (1,2) derivatives were synthesized and characterized by NMR- and IR-spectroscopy and X-ray crystallography. It was demonstrated that titanium dichloride complexes (5–6, 9–12) when treated with MAO, TMA or TIBA are inactive in ethylene polymerization catalysis. However, these compounds become catalytically active in presence of lithium or magnesium chlorides. It was found that the magnitude of the resulting catalytic activity correlates with the following factors: mode of non-transition metals chlorides introduction to the reaction mixture, the nature of activator, and its overall amount. Resulting catalytic activity varied between 54 and 3500 kg PE/mole Ti٠h٠bar. Formed polymer was a linear polyethylene of high and ultrahigh molecular weight (over 5.95 105 g/mole) with high polydispersity index. Possible mechanisms of lithium and magnesium chlorides ability to promote the catalytic process were proposed.

Reaction of 2,8-Bis(o-hydroxyaryl)quinolines with Group 4 Metal Alkyls Resulting in Three Distinct Coordination Modes of the Tridentate Ligand. X-ray Structure of Complexes and Performance as Precursors in Ethylene Polymerization Catalysis

A series of bis(o-hydroxyphenyl)quinolines have been prepared, starting from 2,8-dibromoquinoline. Reaction of these new ligand precursors with group 4 tetrabenzyl complexes MBn4 results in benzyl substitution of the azine fragment with the formation of amide complexes (M = Ti) or amine complexes with an N–H fragment coordinated to the metal (M = Zr, Hf). The third structural type—Zr complexes where the aromatic system of the precursor remains intact—can be prepared through the reaction of the bis(o-hydroxyphenyl)quinolones with 4 mol of methyllithium, followed by ZrCl4. The new complexes result in active polymerization catalysts when activated with MAO/borate cocatalysts on silica supports, resulting in polyethylene copolymers with very high molecular weights and multimodal MWDs.

Direct observation of a cationic ruthenium complex for ethylene insertion polymerization

We report here the first direct observation of a cationic ruthenium complex catalyzing ethylene insertion polymerization. An arene-tethered ruthenium complex (η6-C6H5(CH2)3SCH3RuCl2) (3) was synthesized and shown to be able to catalyze ethylene polymerization upon activation with AlMe2Cl. For mechanistic studies, we synthesized the homologous dimethylated η6-C6H5(CH2)3SCH3Ru(CH3)2 (4) complex, which upon activation with the Brookhart acid ([H(Et2O)2]+ [BAr′4]−) was also active for ethylene insertion polymerization. 1H-NMR and mass spectrometry (MS) studies provide direct evidence for a ruthenium cationic [η6-C6H5(CH2)3SCH3Ru(oligomer)]+ complex as the active species during polymerization. This has unambiguously shown for the first time a ruthenium complex as the active species for catalyzing olefin insertion polymerization.

Coordination compounds of chromium (+3) and vanadium (+3) and (+5) with 2,6-bis(diphenylhydroxymethyl)pyridyl ligand: Synthesis and study of catalytic activity in the polymerization of ethylene

Coordination compounds of chromium (III) and vanadium (III) and (V) with 2,6-bis(diphenylhydroxymethyl)pyridine have been synthesized. Composition and properties of the obtained complexes have been evaluated by NMR, IR spectroscopy, X-ray diffraction, and elemental analysis. Depending on the nature of the metal and the synthesis conditions, there are various types of coordination state of the terdentate pyridine ligand in the obtained complexes: it can bind either as a dianionic, bisalkoxide, terdentate (compounds 5, 7, 8, 9), monoanionic, alkoxide/alkohol, terdentate (compounds 4, 6) or as a neutral, bisalkohol, terdentate ligand (compound 3). Coordination compounds of chromium were found to be incapable of catalytic polymerization of ethylene. Catalytic activity of vanadium (III) and (V) complexes in this reaction varied between 85 and 578kgPE/molVh after activation with diethylaluminum chloride, depending on the V/Al ratio.

(“Ferrocene-salaldiminato”)zirconium Complexes for Ethylene Polymerization Catalysis: The Role of the Bulky Substituents

We prepared the 2-hydroxy-5-trimethylsilylferrocenecarbaldimine systems 13 enantioselectively by a short synthetic route starting from the chiral ferrocene carbaldehyde acetal 5. The imines 13a–c were used to synthesize the zwitterionic (“ferrocene-salaldiminato”)2ZrCl4 complexes 14a–c. Activation with MAO gave homogeneous Ziegler–Natta catalysts, which showed only a moderate ethylene polymerization activity, similar to the unsubstituted parent “ferrocene-salaldiminato” zirconium systems. Consequently, a synthetic route was devised and carried out to make the corresponding 2-hydroxy-3,5-bis(trimethylsilyl)ferrocenecarbaldimines (21) available. The enantiomerically highly enriched ligands (pS)-21a and -d derived from the aldehyde and aniline or cyclohexylamine, respectively, were used to synthesize the corresponding (“ferrocene-salaldiminato”)2ZrCl4 complexes 22a,d. Both gave highly active homogeneous Ziegler–Natta catalysts upon activation with MAO for the formation of linear low molecular weight polyethylene. Complex 22d and many ligand precusors from both sequences were characterized by X-ray diffraction.

Synthesis of copolymers of ethylene and (meth)acrylates or styrene by an original dual radical/catalytic mechanism

Neutral NiII complexes, classically used for catalytic ethylene polymerization, can play an additional role as radical initiators of the homo- and copolymerizations of (meth)acrylates and styrene. Benefiting from this duality, the copolymerization of ethylene and various (meth)acrylates or styrene was successfully performed. Multiblock copolymers containing sequences of both ethylene and (meth)acrylates were prepared for the first time from an original dual radical/catalytic mechanism.

Suppression of β-Hydride Chain Transfer in Nickel(II)-Catalyzed Ethylene Polymerization via Weak Fluorocarbon Ligand–Product Interactions

The synthesis and characterization of two neutrally charged Ni(II) ethylene polymerization catalysts, [2-tert-butyl-6-((2,6-(3,5-dimethylphenyl)phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CH3)FI-Ni) and [2-tert-butyl-6-((2,6-(3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]nickel(II) methyl trimethylphosphine ((CF3)FI-Ni) are reported. In the presence of a Ni(COD)2 cocatalyst, these catalysts produce markedly different polyethylenes: densely branched oligomers with Mw = 1.4 × 103 g mol–1 for (CH3)FI-Ni vs lightly branched polyethylenes with Mw = 92 × 103 g mol–1 for (CF3)FI-Ni and with ∼6.5× the polymerization activity and with much greater performance thermal stability. HOESY 2D 19F,1H NMR spectra of a model Ni-ethyl compound, [2-tert-butyl-6-((2,6-(3,5-bis(trifluoromethyl)phenyl)phenylimino)methyl)phenolato]nickel(II) ethyl 2,4-lutidine ((CF3)FI-Ni-Et), indicate non-negligible Cβ–Hβ···F3C through-space dipolar interactions, and molecular modeling reveals that Cβ–Hβ···...

Synthesis, structures of (aminopyridine)nickel complexes and their use for catalytic ethylene polymerization

A series of α-aminopyridines in the form of (2,6-C(6)H(3)N)(R(1))(CHR(2)NR(3)R(4)) (R(1) = R(2) = H R(3) = H R(4) = (i)Pr (L1a), R(4) = (t)Bu (L1b), R(4) = Ph (L1c), R(4) = 2,6-Me(2)C(6)H(3) (L1d), R(4) = 2,6-(i)Pr(2)C(6)H(3) (L1e), R(1) = R(2) = H R(3) = R(4) = Et (L1f), R(1) = H R(2) = Me R(3) = H R(4) = (i)Pr (L2a), R(4) = Ph (L2c), R(4) = 2,6-Me(2)C(6)H(3) (L2d), R(4) = 2,6-(i)Pr(2)C(6)H(3) (L2e), R(1) = Me R(2) = H R(3) = H R(4) = 2,6-(i)Pr(2)C(6)H(3) (L3e)) and β-aminopyridines in the form of (2-C(6)H(4)N)(CH(2)CH(2)NR(1)R(2)) (R(1) = H R(2) = (i)Pr (4a), R(2) = (t)Bu (L4b), R(1) = R(2) = Et (L4f)) have been prepared. Their corresponding halonickel complexes 1a-4f are synthesized by ligand substitution from (DME)NiBr(2) and the molecular structures are characterized. Four types of coordination modes include four-coordinate mononuclear species with one ligand, five-coordinate mononuclear species with two ligands, five-coordinate dinuclear species with two ligands, and a six-coordinate polymeric framework were determined by X-ray crystallography. Using methylaluminoxanes (MAO) as the activator, the nickel complexes can catalyze ethylene polymerization under moderate pressure and ambient temperature. The activity reaches 10(5) g PE mol(-1) Ni h. The PE products with high branching and high crystallinity have M(n) ~ 10(3) with PDI < 2.

Surface-initiated catalytic ethylene polymerization within nano-channels of ordered mesoporous silicas for synthesis of hybrid silica composites containing covalently tethered polyethylene

A surface-initiated catalytic ethylene polymerization technique is successfully demonstrated herein for the covalent surface-grafting of polyethylene chains within nanochannels of mesoporous silicas to give hybrid mesoporous silica/polyethylene composite materials. In this technique, a Pd−diimine catalyst, [(ArN C(Me)–(Me)C NAr)Pd(Me)(N CMe)] + SbF 6 − (Ar = 2,6-( iPr) 2C 6H 3) ( 1), was first covalently immobilized onto two ordered mesoporous silicas (SBA-15 and MSU-F) containing surface-bound acryloyl functionalities to render the mesoporous silica-supported chelate Pd−diimine catalysts (Pd-SBA15 and Pd-MSUF, respectively). Surface-initiated ethylene polymerizations within mesopores were subsequently carried out with Pd-SBA15 and Pd-MSUF at an ethylene pressure of 400 psi and 5 °C. A mechanistic study on the polymerization behavior and the confining effects of silica meso-structures on polymer growth has been undertaken. The covalent surface-grafting of polyethylene within silica nanochannels was confirmed by the results from Fourier-transformed infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), nitrogen adsorption–desorption, electron microscopy, and proton nuclear magnetic resonance ( 1H NMR). The content of grafted polyethylene in the composites can be adjusted in a wide range by varying polymerization time. This represents the first report on the covalent surface functionalization of mesoporous silicas with polyethylene via surface-initiated ethylene polymerization.

Ethylene Polymerization Catalysis by Vanadium-Based Systems Bearing Sulfur-Bridged Calixarenes

Calixarenes bridged by thia (−S−), sulfinyl (−SO−), or sulfonyl (−SO2−) linkers have been employed as ancillary ligands in vanadium-based ethylene polymerization and in the ring-opening polymerization of ε-caprolactone. For ethylene polymerization, all pro-catalysts [PPh4][VOCl2(R-calix[4]areneH2)] (R = p-tert-butylthia (−S−) (1), sulfinyl (−SO−) (2), sulfonyl (−SO2−) (3)) were highly active, with the system bearing the sulfonyl (−SO2−)-bridged calixarene displaying enhanced activity. The molecular structures of pro-catalysts 2 and 3 are reported. Pro-catalysts 1–3 were inactive for the ROP of ε-caprolactone.

A Novel Al-Bridged Trinuclear Iron(II) Bis(imino)pyridyl Complex with Catalytic Ethylene Polymerization Behavior

A self-assembled Al-bridged diiminopyridine-based ligand (3) was synthesized and characterized by FT-IR, ESI-MS and NMR spectroscopy. Electron spectral titrations were performed to confirm the formation of a novel trinuclear bis(imino)pyridyl iron(II) complex (4) upon addition of <TEX>$FeCl_2$</TEX> into Al-bridged ligand 3 in methanol solution. Simultaneously, a typical bis(imino)pyridine-iron(II) complex (2) was synthesized and fully characterized. The X-ray crystal study of the iron(II) complex 2 disclosed a five-coordinate, distorted square-pyramidal structure with the tridentate N^N^N ligand and chlorides. The optimal molecular structure of 4 was obtained by means of molecular mechanics, which showed that each iron atom in the complex 4 is surrounded by two chlorides, a tridentate N^N^N ligand and one oxygen atom, supporting considerations about the possibility of six-coordinate geometry from MMAO or the ethylene access. A comparison of 4 with the reference 2 revealed a remarkable decrease of the catalytic activity and MMAO consumption (activity up to <TEX>$0.41{\times}10^3\;kg\;{mol_{Fe}}^{-1}h^{-1}bar^{-1}$</TEX>, Al/Fe = 650 for 4 and <TEX>$7.02{\times}10^3\;kg\;{mol_{Fe}}^{-1}h^{-1}bar^{-1}$</TEX>, Al/Fe = 1600 for 2).

Catalytic ethylene polymerization by the titanium-polyhedral oligomeric silsesquioxane-Et3Al2Cl3 system

Titanium (IV) precursors anchored to alkyl substituted polyhedral oligomeric silsesquioxane (POSS) trisilanol and disilanol were prepared and characterized. These catalysts, formulated as [Ti-POSS(O∩O∩O)OPri, 1] and [Ti-(POSS(O∩O))2, 2], were found to be active in the polymerization of ethylene at high temperatures in combination with ethylaluminum sesquichloride (Et3Al2Cl3) as a co-catalyst. The polyethylene products so obtained are linear, crystalline and display narrow dispersities. The effect of various reaction parameters on the catalyst performance is described.

Catalytic polymerization of ethylene in aqueous media

The kinetics of the polymerization of ethylene in aqueous media using a monometallic palladium catalyst containing phosphine ligands was investigated. The catalyst activity was lower than that in toluene and was strongly affected by both the catalyst exposure to water and type of surfactant used. Anionic surfactants may poison of the catalyst, but exposure to water was the main cause of loss of activity. The deactivation of the catalyst by water seemed to occur either before starting the reaction (namely, during the miniemulsification process) or immediately after the catalyst became in contact with ethylene. The molecular weights were not affected by the accessibility of water to the catalyst. A polymerization mechanism was proposed and a mathematical model for the process was developed.

Alkyne-functionalized metallocene complexes: Synthesis, structure, and catalytic ethylene polymerization

Reactions of phenylethynyl lithium with substituted cyclopentenones gave the corresponding pendant phenylethynyl substituted cyclopentadienes. Subsequent deprotonation and transmetallation with TiCl 4·2THF, ZrCl 4, and Cp ∗ZrCl 3 yielded the alkyne-functionalized metallocene complexes [C 5Me 4(C CPh)] 2MCl 2 [M = Ti ( 1), Zr ( 2)], Cp ∗[C 5Me 4(C CPh)]ZrCl 2 ( 3), and Cp ∗[C 5H 2R′ 2(C CPh)]ZrCl 2 [R′ = Me ( 4), Ph ( 5)]. These complexes were fully characterized by 1H NMR, 13C NMR, MS spectra, and elemental analysis. The molecular structure of 2 was determined by single crystal X-ray diffraction analysis. Ethylene polymerization was studied with these complexes in the presence of methylaluminoxane (MAO).