Olefin Polymerization Catalysts Research Articles

Stabilized Vanadium Catalyst for Olefin Polymerization by Site Isolation in a Metal-Organic Framework.

Vanadium catalysts offer unique selectivity in olefin polymerization, yet are underutilized industrially owing to their poor stability and productivity. Reported here is the immobilization of vanadium by cation exchange in MFU-4l, thus providing a metal-organic framework (MOF) with vanadium in a molecule-like coordination environment. This material forms a single-site heterogeneous catalyst with methylaluminoxane and provides polyethylene with low polydispersity (PDI≈3) and the highest activity (up to 148 000 h-1 ) reported for a MOF-based polymerization catalyst. Furthermore, polyethylene is obtained as a free-flowing powder as desired industrially. Finally, the catalyst shows good structural integrity and retains polymerization activity for over 24 hours, both promising attributes for the commercialization of vanadium-based polyolefins.

Stabilized Vanadium Catalyst for Olefin Polymerization by Site Isolation in a Metal–Organic Framework

AbstractVanadium catalysts offer unique selectivity in olefin polymerization, yet are underutilized industrially owing to their poor stability and productivity. Reported here is the immobilization of vanadium by cation exchange in MFU‐4l, thus providing a metal–organic framework (MOF) with vanadium in a molecule‐like coordination environment. This material forms a single‐site heterogeneous catalyst with methylaluminoxane and provides polyethylene with low polydispersity (PDI≈3) and the highest activity (up to 148 000 h−1) reported for a MOF‐based polymerization catalyst. Furthermore, polyethylene is obtained as a free‐flowing powder as desired industrially. Finally, the catalyst shows good structural integrity and retains polymerization activity for over 24 hours, both promising attributes for the commercialization of vanadium‐based polyolefins.

Robust Bulky [P,O] Neutral Nickel Catalysts for Copolymerization of Ethylene with Polar Vinyl Monomers

Several nickel complexes bearing sterically bulky phosphino-phenolate ([P,O]) ligands were synthesized and explored as catalysts for olefin (co)polymerization. In the absence of an activator, the complexes showed very high catalytic activities (up to 107 g molNi–1 h–1) for ethylene polymerization even at 90 °C or with the addition of a large amount of a polar additive (such as ethyl alcohol, diethyl ether, acetone, or even water), affording linear polymers with high molecular weights (up to 6.53 × 105). In contrast, most of the previously reported nickel catalysts suffer from severe activity suppression at elevated temperature. It is rare that a catalyst has so many good performances simultaneously, including high catalytic activity, good tolerance for polar groups, strong thermal stability, and yielding high molecular weight linear polyethylene. Most importantly, these bulky nickel complexes used in this study also effectively copolymerized ethylene with challenging polar vinyl monomers, including commer...

Quality control for Ziegler-Natta catalysis via spectroscopic fingerprinting

Commercial olefin polymerization catalysts are typically produced at a manufacturing site before transport to production facilities for storage and eventual use. During transport and storage, catalysts can deteriorate resulting in decreased catalytic performance due to contact with environmental factors. In this work, a spectroscopic toolbox was developed for quality assurance purposes of a third generation Ziegler-Natta catalyst for ethylene polymerization. A pre-activated, industrial Ziegler-Natta catalyst was exposed singly to heat, dry air, and moisture to study the specific environmental factors. Activity tests were performed with the polymer morphology inspected by SEM and image analysis. Catalyst characterization was conducted using Fourier Transform Infrared spectroscopy with CO and Diffuse Reflectance UV–Vis spectroscopy to relate unique spectroscopic fingerprints to different environmental effects. Reactivity towards gas-phase ethylene polymerization was tested using Diffuse Reflectance Infrared Fourier Transform spectroscopy. This work demonstrates the development of a new spectroscopic methodology useful for quality control in Ziegler-Natta catalysis.

High-precision Molecular Modelling for Ziegler-Natta Catalysts

A major bottleneck of computational chemistry in heterogeneous catalysis is found at the difficulty and resultant inaccuracy of molecular models for catalyst surfaces. Here, we review our recent efforts to establish a high-precision molecular model of heterogeneous Ziegler-Natta catalysts for olefin polymerization, which was mainly based on the validation of potential molecular models for a set of experimentally known facts in density functional calculations. The coadsorption of donor molecules with Ti mononuclear species on MgCl2 surfaces is proposed as an experimentally consistent molecular model, and its successful utilization in a structure-performance relationship study for donors is described.

Designing catalysts for olefin polymerization and copolymerization: beyond electronic and steric tuning

More than 50 years have passed since Ziegler and Natta shared the Nobel Prize in Chemistry for their discovery of olefin polymerization catalysts. The field of metal-catalysed polymerization has since matured, in no small part owing to the development of several high-performance catalysts. Although polymerization research has in many ways been driven by catalyst development, this has often occurred as a result of trial and error discovery of a promising motif, followed by extensive tuning of the steric and electronic properties of the ligand(s) present in the lead complex. Recently, some alternative design strategies have emerged that afforded new classes of olefin polymerization catalysts. This Perspective highlights recently designed catalyst motifs and the novel reactivity patterns they enable. Special attention is given to methods specifically designed for the copolymerization of ethylene with polar-functionalized co-monomers — challenging reactions that showcase these creatively designed catalyst motifs. The development of high-performance olefin polymerization catalysts is a major driving force in polyolefin studies. This Perspective discusses some alternative strategies for catalyst design — strategies in which existing systems are tuned beyond merely modifying the electronic and steric properties.

Catalyst Nuclearity Effects on Stereo- and Regioinduction in Pyridylamidohafnium-Catalyzed Propylene and 1-Octene Polymerizations

In comparison to monometallic controls, bimetallic olefin polymerization catalysts often exhibit superior performance in terms of higher polyolefin Mw, higher comonomer incorporation, and higher polar comonomer tolerance. However, using cooperating catalyst centers to modulate stereoselectivity in α-olefin polymerizations is relatively unexplored. In this contribution, the monometallic Hf(IV) complex, L1-HfMe2 (catalyst A, L1 = 2,6-diisopropyl-N-{(2-isopropylphenyl)[6-(naphthalen-1-yl)pyridin-2-yl]methyl}aniline), and homo-bimetallic Hf(IV) complexes, L2-Hf2Me5 (catalyst B) and L2-Hf2Me4 (catalyst C) (L2 = N,N′-{[naphthalene-1,4-diylbis(pyridine-6,2-diyl)]bis[(2-isopropylphenyl)methylene)]bis(2,6-diisopropylaniline}), are activated with Ph3C+B(C6F5)4– and investigated in propylene and 1-octene homopolymerizations. In propylene polymerizations, the conformationally flexible catalyst B-derived bimetallic dicationic catalyst produces higher Mw polypropylene (up to 7.8×), higher total stereo- and regiodefect densities (up to 3.5×), and lower Tm (by as much as ∼14 °C) versus the monometallic catalyst A-derived control. In 1-octene polymerizations, the conformationally flexible catalyst B-derived bimetallic dicationic catalyst induces greatly reduced isotacticity (23% reduction in [mmmm]) versus the catalyst A-derived monometallic control ([mmmm] > 99%). Interestingly, conformationally flexible catalyst B-derived cationic bimetallic Hf catalysts are also known to undergo rapid intramolecular/intermetal methyl exchange and to exhibit strong Hf···Hf cooperative enchainment effects in ethylene homo- and copolymerizations. Steric effects and intramolecular intermetal chain transfer likely both contribute to the increased isotactic polyolefin stereo- and regiodefect content.

Research Progress of Pre - transition Metal Olefin Polymerization Catalyst for Salicylaldehyde Imine

Salicylaldehyde imine transition metal catalyst is a kind of olefin polymerization catalyst which is widely used in the coordination of salicylaldehyde imine ligand and pre-transition metal. Salicylaldehyde imine ligands have the characteristics of easily insert different substituents via organic synthesize. Therefore, the regulation of the polymerization activity, polymerization product and product distribution can be achieved by changing the steric hindrance effect, electronic effect and the number of metal active sites which near the catalytic active center. The development status of the transition metal catalyst of salicylaldehyde imide was summarized in this paper. The influence of the ligand structure of salicylaldehyde imide transition metal catalyst on the catalytic performance which involved the high selectivity ethylene trimerization, ethylene / α-olefin, / Polar monomer copolymerization, ethylene polymerization production of ultra-high molecular weight polyethylene and many other areas of olefin polymerization was elaborated and providing references for further study and industrial applications of this catalyst.

Triazolecarboxamidate Donors as Supporting Ligands for Nickel Olefin Polymerization Catalysts

To increase the structural diversity of dinucleating platforms that are used in the construction of olefin polymerization catalysts, we are exploring new ligand designs that feature non-alkoxide/phenoxide bridging groups. In the current study, we demonstrate that 1,2,3-triazole-4-carboxamidate donors are excellent N,N-chelators for nickel and can readily bind secondary metal ions. We found that sterically bulky nickel triazolecarboxamidate complexes are active as ethylene homopolymerization catalysts and can afford low molecular weight polyethylene with about 80–130 branches per 1000 carbon atoms. The addition of zinc salts to our nickel complexes led to catalyst inhibition in some cases, which we have attributed to the formation of catalytically inactive mixed-metal species. To circumvent this problem, we anticipate that further elaboration of the triazolecarboxamidate ligand could provide discrete heterobimetallic complexes that will be useful as single-site catalysts with unique reactivity patterns.

The Multifaceted Role of Methylaluminoxane in Metallocene-Based Olefin Polymerization Catalysis

In single-site olefin polymerization catalysis, a large excess of cocatalyst is often required for the generation of highly active catalysts, but the reason for this is unclear. In this work, fundamental insight into the multifaceted role of cocatalyst methylaluminoxane (MAO) in the activation, deactivation, and stabilization of group 4 metallocenes in the immobilized single-site olefin polymerization catalyst was gained. Employing probe molecule FT-IR spectroscopy, it was found that weak Lewis acid sites, inherent to the silica-supported MAO cocatalyst, are the main responsible species for the genesis of active metallocenes for olefin polymerization. These weak Lewis acid sites are the origin of AlMe2+ groups. Deactivation of metallocenes is caused by the presence of silanol groups on the silica support. Interaction of the catalyst precursor with these silanol groups leads to the irreversible formation of inactive metallocenes. Importantly, a high concentration of MAO (14 wt% Al) on the silica support is necessary to keep the metallocenes immobilized, hence preventing metallocene leaching and consequent reactor fouling. Increasing the loading of the MAO cocatalyst leads to larger amounts of AlMe2+, fewer silanol groups, and less metallocene leaching, which all result in higher olefin polymerization activity.

Facile in situ generation of highly active (arylimido)vanadium(v)-alkylidene catalysts for the ring-opening metathesis polymerization (ROMP) of cyclic olefins by immediate phenoxy ligand exchange.

Highly active catalysts for the ring-opening metathesis polymerization (ROMP) of cyclic olefins (norbornene, cyclopentene, cycloheptene) can be generated in situ by premixing V(CHSiMe3)(NC6F5)(O-2,6-iPr2C6H3)(PMe3)2 (1) with 1.0 equiv. of C6F5OH or C6Cl5OH via the immediate phenoxy exchange; the activity was affected by the kind of phenol added [activity (TOF) in the ROMPs of norbornene: 46 200 min-1 (upon addition of C6F5OH) vs. 37.3 min-1 (by 1)].

Tailoring 2D and 3D molecular sieves structures for polyolefin composites: do all roads lead to remarkable performances?

Multiple synthetic strategies were performed in order to tether a zirconium-based catalyst to the 2D and 3D molecular sieves for olefin polymerizations. The anchoring of fluorene silane to the mesoporous MCM-41 was performed in order to obtain a stable catalyst for olefin polymerization (1@MCM-41). Using spectroscopic methods, this system was shown to have the metal center locked on a face down conformation with the surface. Also, immobilized zirconium complexes have been prepared on three different types of aminopropyl-modified supports (2@magadiite, 2@MCM-41 and 3@MCM-48). The advantage of this latter method of immobilization would be the reduction of the steric effect caused by the support: the catalyst, distant from the surface, is more exposed to the monomer and this situation may lead to an increase in the catalytic activity compared to 1@MCM-41. However, a medium size chain as a spacer between the support and the metallocene is still flexible enough to bend and predisposes the metal center to interact with the support surface; this effect is more evident when the nature of the support is of fixed pore dimensions. These supported catalysts exhibited activity for ethylene polymerization, resulting in linear PEs with high melting temperatures. In order to retain a metallocene assembled as in a homogeneous environment, a multi-step reaction was investigated (4@magadiite) but it led to the leaching of the organic moieties from the surface during catalyst preparation. The best catalytic performance was achieved when homogeneous Oct-amido catalyst (5) was reacted with the surface of magadiite and n-alkyl-AlPO-kan.

Photochemical regulation of a redox-active olefin polymerization catalyst: controlling polyethylene microstructure with visible light

The utility of photoredox chemistry is expanded to include microstructural control of polyolefins.

Distinctive Stereochemically Linked Cooperative Effects in Bimetallic Titanium Olefin Polymerization Catalysts

The complex (μ-Me2C-3,3′){(η5-cyclopentadienyl)[1-Me2Si-(tBuN)](TiMe2)}2 (3) was prepared as a new binuclear catalyst motif for homogeneous olefin polymerization. Complex 3 exists as rac-3 and meso-3 diastereomers, which can be separated and characterized by solution NMR spectroscopy and single-crystal X-ray diffraction. While meso-3 has high thermal stability, rac-3 undergoes thermolysis in solution to quantitatively form the dimeric methylidene complex (μ-Me2C-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)][(μ-CH2)Ti]}2 (rac-4). Activation of rac-3 and meso-3 with 1 equiv of Ph3C+B(C6F5)4– yields [(μ-CMe2-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)(μ-CH3)Ti2]+B(C6F5)4– (5; rac-5 and meso-5, respectively). Interestingly, meso-5 is stable in the presence of an additional 1 equiv of Ph3C+B(C6F5)4–, while rac-5 reacts to yield rac-[(μ-CMe2-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)[(TiCH3)(Ti-η1-Ph3C)]2+[B(C6F5)4–]2 (rac-6) as indicated by multinuclear NMR spectroscopy and DFT computation. meso-3 reacts with 2 equiv of B(C6F5)3 to yield meso-[(μ-CMe2-3,3′){(η5-cyclopentadienyl)[1-Me2Si(tBuN)]}2(μ-CH2)(μ-CH3)Ti2]+MeB(C6F5)3– (meso-7) containing the same meso-5 cation but with a MeB(C6F5)3–counteranion. These findings, along with catalytic results, indicate that rac-3 and meso-3 remain structurally intact during polymerization, consistent with the observed diastereoselectivity effects. Under identical ethylene/1-octene copolymerization conditions, only activated bimetallic rac-3 produces appreciable polymer, with meso-3 exhibiting low activity, but both yield polymer with a branch density >2× that of the monometallic control [(3-tBu-C5H3)SiMe2NtBu]TiMe2 (Ti1). In ethylene/styrene copolymerizations, rac-3 produces polymers with 3.1× higher Mn and 2.1× greater styrene incorporation versus Ti1, while meso-3 catalyzes only ethylene-free styrene homopolymerization. In 1-octene homopolymerizations, meso-3 + B(C6F5)3 (i.e., meso-7) produces highly isotactic poly-1-octene (mmmm 91.7%), while rac-3 + Ph3C+B(C6F5)4– (i.e., rac-5), rac-3 + B(C6F5)3 (i.e., rac-7), and meso-3 + Ph3C+B(C6F5)4– (i.e., meso-5) produce only atactic poly-1-octene. These bimetallic polymerization catalysts exhibit distinctive cooperative effects influencing product Mn, tacticity, and comonomer selection, demonstrating that binuclear catalyst stereochemical factors are significant.

Mitigating chain‐transfer and enhancing the thermal stability of co‐based olefin polymerization catalysts through sterically demanding ligands

ABSTRACTSterically demanding Fe‐ and Co‐based olefin polymerization catalysts 2‐Fe and 2‐Co bearing 2,6‐bis(biphenylmethyl)‐4‐methylaniline substituted bis(imino)pyridine ligands were synthesized and evaluated for ethylene polymerization. The late‐transition metal complexes were characterized by X‐ray diffraction, NMR spectroscopy, and HRMS, while their resultant polymers were characterized by size‐exclusion chromatography and 1H NMR spectroscopy. While catalyst 2‐Fe was inactive, catalyst 2‐Co was found to polymerize ethylene and avoid any detectable chain‐transfer to aluminum events that are known to plague other Fe‐ and Co‐based catalyst systems and to limit molecular weight. Furthermore, 2‐Co displays virtually perfect thermal stability up to 80 °C and shows greatly enhanced thermal stability at 90 °C as compared to previously reported analogues. These observations are attributed to the extreme steric demand imposed by the ligand which mitigates catalyst transfer, deactivation, and decomposition reactions. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 3990–3995

Combined Experimental and Theoretical Approach for Living and Isoselective Propylene Polymerization

The controlled polymerization of propylene with living catalysts in an isoselective fashion with high activities is a continuing challenge for catalysis, with at least one of these properties suffering in most existing systems. Through experimental and theoretical studies, the pyridylamidohafnium olefin polymerization catalysts have been optimized for living behavior, isoselectivity, and activity of propylene polymerization (Đ = 1.2, [m4] = 91%, TOF = 25 000 h–1). Substitution of the bridgehead position with geminal dimethyl substituents forces the stereoselective elements of the catalyst into closer proximity with the active site through a “buttressing effect” while simultaneously preserving symmetry in the catalyst after activation and the first monomer insertion into the Hf–Caryl bond of the ligand. Propagation was shown to be favored over termination through beta-hydrogen transfer to the monomer through a combination of theoretical modeling and experimental monitoring of the reaction which showed a li...

Synthesis of ArOTiCl 3 complexes and their application for ethylene polymerization and copolymerization

In this article, novel olefin polymerization catalyst with lower cost and simple synthetic process were developed, ArOTiCl3 complexes [(2-OMeC6H4O)TiCl3(C1), (2,4-Me2C6H3O)TiCl3(C2), TiCl3(1,4-OC6H4O)TiCl3 (C3), TiCl3(1,4-OC6H2O-Me2-2,5) TiCl3(C4)] and corresponding (ArO)2TiCl2 complexes [TiCl2(OC6H4-OMe-2)2(C5) and TiCl2(OC6H3-Me2-2,6)2(C6)] have been synthesized by the reaction of TiCl4 with phenol, all these complexes were well characterized with 1H NMR,13C NMR, MASS and EA. When combined with methylaluminoxane (MAO), the ArOTiCl3 / MAO system shows high activity for ethylene copolymerization with 1-octene and copolymer was obtained with broaden molecular weight distribution (MWD). The 13C NMR result of polymer indicates that the 1-octene incorporation in polymer reached up to 8.29 mol%. The effects of polymerization temperature, concentration of polymerization monomer and polymerization time on the catalytic activity have been investigated.

Effects of the Linking of Cyclopentadienyl and Ketimide Ligands in Titanium Half‐Sandwich Olefin Polymerization Catalysts

AbstractThe role of the ketimide ligand geometry in Ti half‐sandwich complexes and the consequent effects in olefin polymerization catalysis (ethylene, styrene, 1‐hexene polymerization, and ethylene/1‐hexene copolymerization) were investigated under various conditions. [CpTiCl2(N=CtBu2)] (1; Cp=η5‐cyclopentadienyl) was used as a reference compound for comparison with the recently described complex [{η5‐C5H4CMe2CMe2C(tBu)=N‐κN}TiCl2] (2 a) and a new derivative that has a longer linker between Cp and the ketimide, [{η5‐C5H4CH2CH2CMe2C(tBu)=N‐κN}TiCl2] (9). The presence of a distorted intramolecularly tethered ketimide moiety reduces the polymerization activity significantly in systems that contain Al‐based cocatalysts (methylaluminoxane, triisobutylaluminum). However, in Al‐free systems both types of compounds provided active polymerization catalysts. Notably, the recently reported activation system Et3SiH/B(C6F5)3 was for the first time demonstrated to activate Ti complexes for ethylene and 1‐hexene (co)polymerization catalysis by hydride transfer.

Monometallic and Bimetallic Titanium κ1-Amidinate Complexes as Olefin Polymerization Catalysts

A series of cyclopentadienyl-κ1-amidinate titanium complexes Cp*Ti{NC(ArR)NiPr2}Me2 (ArR = 4-C6H4R, where R = H (1-Me), CF3 (5-Me), tBu (6-Me), or NMe2 (7-Me)) with different para-substituents in the amidinate ligand were synthesized and structurally characterized, along with three bimetallic analogues: 1,4-C6H4{C(NiPr2)N}2{Cp*TiMe2}2 (2-Me), 1,3-C6H4{C(NiPr2)N}2{Cp*TiMe2}2 (3-Me), and CH2{1,4-C6H4-C(NiPr2)N}2{Cp*TiMe2}2 (4-Me). 13C NMR spectroscopy, density function theory, and the quantum theory of atoms-in-molecules were used to evaluate the donor ability of the various NC(Ar R)NiPr2 ligands and the influence of the ArR group para-substituents. Reactions of 1-Me and certain homologues, as well as 2-Me, with borate and borane reagents [CPh3][BArF4] (ArF = C6F5), BArF3, in the absence or presence of Lewis bases or polar unsaturated substrates were carried out, forming adducts and migratory insertion products such as [Cp*Ti{NC(Ph)NiPr2}Me(THF)][BArF4], [Cp*Ti{NC(Ph)NiPr2}{MeC(NiPr)2}][BArF4], and [1,4-C6H...

Novel cationic rare earth metal alkyl catalysts for precise olefin polymerization

ABSTRACTThis mini‐review provides recent progress in the synthesis of rare earth metal dialkyl complexes and their application as highly efficient and regio‐/stereoselective catalysts in the coordination‐insertion (co)polymerization of olefins such as styrene, isoprene, 1,3‐cyclohexadiene, and ocimene. Through modifying the coordination atom, the ligand skeleton, and the substitutent on the skeleton of the chelating ligand, tuning the electron density and the steric environment around the rare earth metal center, the precise control of the activity and regio‐/stereoselectivity of the (co)polymerization as well as the comonomer incorporation and sequence distribution of the resulting copolymers are achieved. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017, 55, 2271–2280