Ethylene Homopolymerization Research Articles

Zirconium and Hafnium Complexes Bearing Tridentate ONN-Ligands: Extremely High Activity toward Ethylene (Co)Polymerization.

The pursuit of high-performance catalysts in the realm of polyolefins is a constant goal. In this study, a range of zirconium (1-ZrCl3, 2-ZrCl3, 3-ZrCl4, 12-Zr) and hafnium (1-HfCl3, 12-Hf) complexes featuring phenoxy-imine-amine ONN-ligands (2,6-R2-C6H3-NH-C6H4-N═CH-C6H2-3,5-tBu2-OH; 1-L: R = H; 2-L: R = F; 3-L: R = iPr) were synthesized and characterized using NMR spectroscopy, as well as single-crystal X-ray diffraction for 2-ZrCl3, 3-ZrCl4, and 12-Zr. These Zr and Hf complexes exhibited remarkable efficiency for ethylene homopolymerization and copolymerization with 1-octene when paired with MAO as the cocatalyst. Notably, the Zr complexes outperformed the Hf complexes with the same ligand, underscoring the substantial impact of the metal center on catalytic performance. The substituents and coordination modes of the ligands also exerted significant influence on the catalytic behavior, affecting both the activity and properties of the resulting polymers. Particularly noteworthy was the exceptional activity of 1-ZrCl3, achieving activity as high as 6.30 × 108 g(PE)·mol-1(Zr)·h-1 for ethylene homopolymerization and generating bi- or multimodal distribution polyethylene. The activation of 1-ZrCl3 by 5 or 20 equiv of d-MAO afforded a dinuclear Zr complex bridged by two chlorides (μ-Cl2-(1-ZrCl2)2), which was analyzed and confirmed by in situ 1H NMR spectroscopy and single-crystal X-ray diffraction.

Melt strain hardening of polymeric systems increasing with decreasing elongational rate: Experimental results and discussion of models

Melt strain hardening is a special feature of polymer materials and polymeric systems relevant for applications and fundamental insights into rheological properties. Strain hardening is dependent on the molecular structure of materials and deformation parameters. This paper deals with literature results of materials exhibiting strain hardening increasing with decreasing elongational rate opposite to most of common polymers. Such a behavior is found for ionomers and polymers with hydrogen bonding, and electrostatic molecular interactions are discussed as the physical origin. Furthermore, layered composites of non-strain hardening polymers are presented that can be rendered strain hardening by introducing compatibilizers or increasing the effect of interfacial tension between two layers by using multilayer arrangements. The strain hardening behavior of polypropylene/high density polyethylene blends of various compositions is discussed. Measurements on ethylene/α-olefin copolymers showing strain hardening significantly increasing with decreasing rate in contrast to linear ethylene homopolymers are described, and it is hypothesized that this behavior is due to a heterogeneous molecular structure with large differences of molar masses of the components.

The third compound promoted ethylene homopolymerization and copolymerization with 1-octene by using metallocene catalyst

The third compound promoted ethylene homopolymerization and copolymerization with 1-octene by using metallocene catalyst

Nickel-Catalyzed Ethylene Copolymerization with Vinylalkoxysilanes: A Computational Study.

Since the discovery of α-diimine catalysts in 1995, an extensive series of Brookhart-type complexes have shown their excellence in catalyzing ethylene polymerizations with remarkable activity and a high molecular weight. However, although this class of palladium complexes has proven proficiency in catalyzing ethylene copolymerization with various polar monomers, the α-diimine nickel catalysts have generally exhibited a much worse performance in these copolymerizations compared to their palladium counterparts. Recently, Brookhart et al. reported a notable exception, demonstrating that α-diimine nickel catalysts could catalyze the ethylene copolymerization with some vinylalkoxysilanes effectively, producing functionalized polyethylene incorporating trialkoxysilane (-Si(OR)3) groups. This breakthrough is significant since Pd-catalyzed copolymerizations are commercially less usable due to the high cost of palladium. Thus, the utilization of Ni, given its abundance in raw materials and cost-effectiveness, is a landmark in ethylene/polar vinyl monomer copolymerization. Inspired by these findings, we used density functional theory (DFT) calculations to investigate the mechanistic study of ethylene copolymerization with vinyltrimethoxysilane (VTMoS) catalyzed by Brookhart-type nickel catalysts, aiming to elucidate the molecular-level understanding of this unique reaction. Initially, the nickel complexes and cationic active species were optimized through DFT calculations. Subsequently, we explored the mechanisms including the chain initiation, chain propagation, and chain termination of ethylene homopolymerization and copolymerization catalyzed by Brookhart-type complexes. Finally, we conducted an energetic analysis of both the in-chain and chain-end of silane enchainment. It was found that chain initiation is the dominant step in the ethylene homopolymerization catalyzed by the α-diimine Ni complex. The 1,2- and 2,1-insertion of vinylalkoxysilane exhibit similar barriers, explaining the fact that both five-membered and four-membered chelates were identified experimentally. After the VTMoS insertion, the barriers of ethylene reinsertion become higher, indicating that this step is the rate-determining step, which could be attributed to the steric hindrance between the incoming ethylene and the bulky silane substrate. We have also reported the energetic analysis of the distribution of polar substrates. The dominant pathway of chain-end -Si(OR)3 incorporation is suggested as chain-walking → ring-opening → ethylene insertion, and the preference of chain-end -Si(OR)3 incorporation is primarily attributed to the steric repulsion between the pre-inserted silane group and the incoming ethylene molecule, reducing the likelihood of in-chain incorporation.

Industrial Data Modeling With Low-Dimensional Inputs and High-Dimensional Outputs

Data-driven modeling will be complicated for a process if the output quality indices are defined in a high-dimensional space, e.g., a quality distribution. In this work, a novel probabilistic modeling method is proposed for industrial processes with low-dimensional inputs and high-dimensional outputs. First, based on a limited sample set, the variational autoencoder (VAE) is applied to extract features of the high-dimensional outputs. Next, a Gaussian Process (GP) model is established on the sub-manifold space defined by the low-dimensional features, and the high-dimensional predictions can be obtained through the VAE reverse procedure. Finally, a deep composing kernel strategy is developed to capture the nonlinearity and correlation hidden in the features. It can significantly improve the generalization performance of the GP model. The effectiveness of the proposed modeling algorithm is demonstrated by applications in a continuous crystallizer system and an ethylene homo-polymerization system.

Influence of the reaction conditions on the Ziegler-Natta catalyzed ethylene polymerization: Kinetics and properties of the resulting polymers

This work conducts an investigation into how the polymerization conditions affect the kinetics of ethylene homopolymerization and the properties of the final polyethylene using a commercially available Ziegler-Natta catalyst with the formula TiCl4/MgCl2. By employing a mathematical model, we estimated the apparent propagation (kp), activation (ka), and deactivation (kd) rate constants under different reaction conditions, including cocatalyst and catalyst concentration, hydrogen/ethylene ratio, and polymerization temperature. Additionally, we examined the properties of the resulting polyethylene products, such as particle size, molecular weight (Mw), melting temperature, and % crystallinity. We found that the trend of polymer particle size was similar to that of the propagation rate constant under the employed polymerization conditions. Our results indicated that parameters enhancing the polymerization rate also increased kp and reduced crystallinity. The quantitative rate constants and polymer characteristics reported in this study provide valuable insights for industrial polyethylene manufacturers, allowing them to fine-tune plant operation conditions and achieve precise control over polymer particle properties. Furthermore, Density Functional Theory (DFT) calculations provided additional insights into the polymerization process, particularly regarding the role of hydrogen as a chain transfer agent and the fundamental significance of MgCl2, emphasizing the need for a minimal-dimensional model to evaluate this role.

Synthesis and characterization of oxazoline-amine zirconium complexes for ethylene homo- and co-polymerization catalysis

The development of group IV catalysts for homogeneous olefin polymerizations is crucial for both industrial and academic research. In this study, we present the synthesis and full characterization (1H NMR, 13C NMR, Elem. Anal. and X-ray) of a new class of oxazoline-amine zirconium complexes. When used in combination with Ph3C+−B(C6F5)4 as the cocatalyst in the absence of scavenger, these complexes show high activity (up to 29.5 kg/(mol·min·atm)) in ethylene homopolymerization giving PE with Mw up to 392.4 kg/mol. On average, these complexes generate less than one polymer chain per catalyst, and negligible olefinic end groups were observed by NMR, both suggesting the absence or lack of chain transfer during polymerization. Furthermore, these complexes are also effective in ethylene/1-octene copolymerization, showing activity up to 42.9 kg/(mol·min·atm) and octene enchainment ratio up to 25.2 mol%. Gradually increasing the reaction time from 1 to 15 min leads to an increase in polymer Mw, chains/cat (up to 14.4) and a decrease in activity. Octene incorporation ratio increases from 12.6 to 17.9 mol% over reaction time (1 to 5 min) at 50 °C, likely suggesting mass transfer limitations at long reaction times. Increasing temperature from 50 °C to 90 °C leads to reduced activity and product Mw (> 5 ×), and increased chains/cat (≈5 ×) in the copolymerization. Olefinic end group analysis by 1H NMR suggests β-H elimination/transfer occurs after octene 2,1-insertion (vinylene; predominant), ethylene insertion (vinyl) and octene 1,2-insertion (vinylidene) at high temperatures.

Heterocene-catalyzed ethylene/oct-1-ene copolymerization under MAO-free and low-MAO conditions: The synthesis of highly statistical copolymers and their use in blending with HDPE

Sandwich SiMe2-bridged ansa-complexes of zirconium, containing heterocycle-fused η5-cyclopentadienyls, derivatives of 2,5-dimethyl-7H-cyclopenta[1,2-b:4,3-b']dithiophene (2), 5,10-dihydroindeno[1,2-b]indole (3) and 5,6-dihydroindeno[2,1-b]indole (4) – 'heterocenes' – catalyzed ethylene homopolymerization and ethylene/oct-1-ene (E/O) copolymerization in the presence of triisobutylaluminum (TIBA) without MAO and perfluoroaryl borate activators, the benchmark bis(η5-fluorenyl) complex 1 was virtually inactive under these conditions. In the absence of MAO, E/O copolymerization resulted in a formation of copolymers not containing EOOE fragments even at E/O ratio of 2.4. Addition of 10 eq. of MMAO-12 resulted in increase of both catalytic activities of 2–4 and oct-1-ene incorporation. E/O copolymers POE-05 (obtained on TIBA activated precatalyst 2) and POE-17 (obtained on TIBA/MMAO-12 activated precatalyst 4) were not inferior to the best commercial E/O copolymers in physico-mechanical characteristics at −45 °C. Extrusion blends of POE-05 and POE-17 with high density polyethylene (HDPE) demonstrated high impact strength and frost resistance.

Synthesis of Si‐O‐Si bridged diamido Group 4 complexes and the applications to polymerization of olefins

Titanium, zirconium, and hafnium complexes O[Me2Si(Dip)N]2MCl2 [Dip = 2,6‐iPr2C6H3; M = Ti (1), Zr (2), Hf (3)], O[Me2Si(tBu)N]2ZrCl2 (4), and O[iPr2Si(Dip)N]2ZrCl2 (5) supported by Si‐O‐Si bridged diamido ligands were synthesized. X‐ray diffraction analysis disclosed that complex 2 displays a distorted trigonal bipyramidal geometry. Complexes 1–5, upon the activation with sMAO, exhibited diverse catalytic performance for the polymerization of ethylene and copolymerization of ethylene with norbornene or 1‐octene. For ethylene homopolymerization, both complexes 1–2 are good catalysts giving polymer with high molecular weight and narrow polydispersities. Complex 2 catalyzed copolymerization of ethylene with 1‐octene exhibiting high catalytic activity but with norbornene showing moderate activity, affording corresponding high molecular weight copolymers with relatively high comonomer incorporations of 11% and 29%, respectively.

A tridentate phenoxy-phosphine (POP) divalent chromium complex and its reactivities in olefin polymerization

We reported the synthesis and characterization of a Cr(ii) complex based on a tridentate phenoxy-phosphine ligand and studied its reactivities in ethylene and norbornene homopolymerization and ethylene copolymerization with norbornene or 1-octene.

Cationic Ni(II) Species and Their Application in Olefin Polymerizations

[(η3-Allyl-Me)Ni(mesitylene)][BArF4] (allyl-Me = C3H4-2-Me (η3-methallyl); BArF4 = B(3,5-(F3C)2C6H3)4; 1) was treated with the phosphine ligands tBu3P, Ad3P (Ad = tri-1-adamantylphosphine), and TMPP (TMPP = tris(2,4,6-trimethoxyphenyl)phosphine). Although these phosphines display similar steric bulk and differ only moderately in their electronic properties, very different reaction products are isolated. For tBu3P, only the phosphonium salt [tBu3P-C3H4-2-Me][BArF4] (2) is formed; this contrasts with the reactivity with TMPP, in which the mesitylene ligand is readily displaced to yield [(η3-allyl-Me)Ni(tmpp)][BArF4] (3). With Ad3P, we observe the formation of an unusual C–H bond activation product [(toluene)Ni(κC:P-C10H14–PAd2][BArF4] (4). Nevertheless, Ad3P successfully stabilizes the two-coordinate Ni(I) species [(Ad3P)2Ni][BArF4] (5). Complexes 3–5 have been evaluated in the homopolymerization of ethylene and norbornene after addition of the Lewis acid B(C6F5)3.

Palladium(II) Complexes with the 4,5‐Bis(diphenylphosphino)acenaphthene Ligand and Their Reactivity with Ethylene

AbstractThe last two decades have witnessed the development of homogeneous catalysts for ethylene homo‐ and co‐polymerization reactions based on late transition metals. When Pd(II) is the metal of choice, the best ligand‐metal combination deals with either bidentate nitrogen‐donor molecules or phosphinobenzene sulfonate derivatives. In this contribution we have investigated the coordination chemistry to Pd(II) of a bidentate phosphorus ligand, namely 4,5‐bis(diphenylphosphino)acenaphthene (1). Starting from the neutral complex, [Pd(1)(CH3)Cl], we obtained the cationic derivatives [Pd(1)(CH3)(L)][SbF6], with L being either CH3CN or 3,5‐lutidine. Using in situ NMR spectroscopy we investigated the reaction of [Pd(1)(CH3)(NCCH3)][SbF6] with ethylene, at room temperature, and ambient ethylene pressure. We discovered that [Pd(1)(CH3)(NCCH3)][SbF6] acts as a catalyst for butenes and hexenes synthesis with the relevant Pd‐ethyl intermediate as the catalyst resting state. At the same time the color of the solution turned from pale yellow to light red due to the formation of the dinuclear species [Pd(μ‐η2−C6H5)PPh)−PPh2]2[SbF6]2. Both the neutral Pd(II) complex, activated in situ by NaSbF6, and the monocationic acetonitrile derivative were tested in the ethylene homopolymerization reaction at high pressure, leading to low molecular weight, branched, polyethylene.

New Ways for Controlling the Molecular-Weight Characteristics and Branching Distribution in Polyethylene Obtained over Supported Catalysts Containing Bis(imino)pyridyl Complexes of Fe(II) and Bis(imine) Complexes of Ni(II)

The paper describes ways for controlling the molecular structure of polyethylene (PE) produced over supported catalysts containing bis(imino)pyridyl complexes of Fe(II) (LFeCl2) and bis(imine) complexes of Ni(II) (*LFeCl2), which are anchored on silica gel modified by the introduction of alumina (SiO2(Al)). Under variation of polymerization conditions over LFeCl2 /SiO2(Al) catalysts, linear PE with different molecular weight and controllable molecular-weight distribution (MWD) was obtained. Homopolymerization of ethylene over *LNiBr2 /SiO2(Al) catalysts led to the formation of branched PE with the molecular-weight and thermophysical characteristics close to the low-density polyethylene produced by ethylene copolymerization with α-olefins over supported metallocene catalysts and supported Zieglertype catalysts. A method was proposed for constructing the supported bicomponent catalysts containing LFeCl2 and *LNiBr2 complexes anchored on the SiO2(Al) support for the deliberate production of polyethylene with the required molecular structure. There are examples of obtaining the linear PE with bimodal MWD on a bicomponent supported catalyst containing two different LFeCl2 complexes, the PE with controllable branching distribution on a bicomponent catalyst synthesized by anchoring LFeCl2 and *LNiBr2 complexes on the SiO2(Al) support, and an example of modifying the industrial chromium oxide catalyst by introducing the LFeCl2 complex for the control of MWD and branching distribution in the produced polyethylene.

Titanium Complexes Bearing NNO‐Tridentate Ligands: Highly Active Olefin Polymerization Catalysts with Great Control on Molecular Weight and Distribution†

Comprehensive SummaryA series of titanium amido complexes (1‐Ti(NMe2)2 to 4‐Ti(NMe2)2) bearing NNO‐tridentate ligands was synthesized from the reactions of phenoxy‐imine‐amine ligands with one equivalent of Ti(NMe2)4. Subsequently, titanium dichloride complexes (1‐TiCl2 to 4‐TiCl2) were prepared by treatment of titanium amido complexes with excess Me3SiCl in toluene. All metal complexes were characterized by 1H and 13C NMR spectroscopy, and the molecular structures of complexes of 2‐Ti(NMe2)2, 2‐TiCl2, and 4‐TiCl2 in the solid state were determined by single‐crystal X‐ray diffraction. Upon activation with MAO, titanium dichloride complexes as single‐site catalysts were extremely active toward ethylene homopolymerization with great control on molecular weight and distribution. In particular, 3‐TiCl2/MAO exhibited an activity as high as 1.35 × 108 g(PE)·mol−1(Ti)·h−1 at 70°C and produced polyethylene with high molecular weight (41.7 × 104 g∙mol−1) and very narrow distribution (Đ = 1.23). In the presence of 1‐octene as comonomer, linear low‐density polyethylenes (LLDPEs) with ultrahigh molecular weights (Mw = 136—326 × 104 g∙mol−1) and narrow distributions (Đ = 1.20—1.50) were successfully synthesized.

Nickel Catalysts for Non‐Alternating CO‐Ethylene Copolymerization

AbstractTransition metal‐catalyzed copolymerization of CO and ethylene has a strong inherent propensity to produce the strictly alternating copolymer. In this work, nickel catalysts capable of both homopolymerization of ethylene and alternating copolymerization of CO and ethylene are developed to explore the possibility of non‐alternating copolymerization of CO and ethylene under the assumption that comonomer incorporation in the polymer chain can be adjusted by the concentrations of the comonomers. Both polyketones with slightly more than 50 % ethylene and “polyethylenes” with a small amount of CO incorporation are obtained but only under carefully controlled conditions and in low yields.

Effect of Mono- and Multichlorinated Organic Compounds-Chlorocyclohexane and Hexachloro-p-xylene-On the Catalytic Properties of Titanium-Magnesium Catalysts in the Homo- and Copolymerization of Ethylene with 1-Hexene.

Ethylene polymerization and ethylene/1-hexene copolymerization over the titanium–magnesium catalytic system in the presence of chlorocyclohexane (CHC) and hexachloro-p-xylene (HCPX) has been studied. Modification of TMC with chlorocyclohexane and hexachloro-p-xylene increased catalyst activity severalfold for both ethylene polymerization and ethylene/1-hexene copolymerization. The key kinetic regularities of ethylene homopolymerization and ethylene/1-hexene copolymerization in the presence of CHC and HCPX were determined, and the copolymerization constants were measured. Molecular characteristics and the copolymer composition were determined for the synthesized samples of ethylene homopolymers and ethylene/hexene copolymers. Modification of the titanium–magnesium catalyst with chlorinated organic compounds reduced 1-hexene content in the copolymer; polymerization was sensitive to 1-hexene as a regulator of polymer molecular weight. The potential mode of action of chlorinated organic modifiers on catalytic properties of titanium–magnesium catalyst is discussed.

Slurry Homopolymerization of Ethylene Using Thermostable α-Diimine Nickel Catalysts Covalently Linked to Silica Supports via Substituents on Acenaphthequinone-Backbone.

Four supported α-diimine nickel(II) catalysts covalently linked to silica via hydroxyl functionality on α-diimine acenaphthequinone-backbone were prepared and used in slurry polymerizations of ethylene to produce branched polyethylenes. The catalytic activities of these still reached 106 g/molNi·h at 70 °C. The life of the supported catalyst is prolonged, as can be seen from the kinetic profile. The molecular weight of the polyethylene obtained by the 955 silica gel supported catalyst was higher than that obtained by the 2408D silica gel supported catalyst. The melting points of polyethylene obtained by the supported catalysts S-C1-a/b are all above 110 °C. Compared with the homogeneous catalyst, the branching numbers of the polyethylenes obtained by the supported catalysts S-C1-a/b is significantly lower. The polyethylenes obtained by supported catalyst S-C1-a/b at 30–50 °C are free-flowing particles, which is obviously better than the rubber-like cluster polymer obtained from homogeneous catalyst.

Controlled Cobalt-Mediated Free-Radical Co- and Terpolymerization of Carbon Monoxide.

While controlled free-radical polymerizations are established for a vast range of vinyl monomers, they have not been reported for carbon monoxide, although it is a unique monomer that forms in-chain keto groups which can promote, for example, desirable photo-degradability in polyethylenes. We report organometallic-mediated radical copolymerization of carbon monoxide with ethylene initiated by an organocobaltIII compound to keto-modified polyethylenes with up to 15 mol % ketone repeat units. Terpolymerization with 2-methylene-1,3-dioxepane affords polyethylenes with in-chain ester and keto groups. Compared to ethylene homopolymerization, the controlled character of the copolymerization is strongly enhanced by the Lewis base function of carbon monoxide, which suppresses multiple unfavorable termination pathways.

Synthesis, molecular structure and catalytic performance of heterocycle-fused cyclopentadienyl-amido CGC of Ti (IV) in ethylene (co)polymerization: The formation and precision rheometry of long-chain branched polyethylenes

Long-chain branching is an efficient tool to design and produce polyolefins with enhanced mechanical characteristics, physical properties, and processability. In the synthesis of long-chain branched polyethylene (LCB PE), constrained geometry complexes (CGCs) of Ti (IV) [(η5-C5Me4)SiMe2NtBu]TiX2 (X = Cl, Ti1; X = alkyl) are highly effective at elevated temperatures. However, further development of polyolefin technologies requires new catalytic approaches to provide LCB formation in broad temperature interval. In the present study, a series of CGCs of Ti (IV) of general formula [Cp#SiMe2NtBu]TiCl2 derived from heterocycle-fused cyclopentadienes Cp# (Ti2–Ti5) were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis (XRD). New complexes Ti2–Ti5 along with benchmark precatalysts (n-BuC5H4)2ZrCl2 (Zr1) and Ti1 were supported on MMAO-12/silica and investigated in ethylene homopolymerization and ethylene/hex-1-ene copolymerization. In contrast to benchmark complexes Ti1 and Zr1, Ti2–Ti5 catalyzed formation of LCB PEs even at 80 °C, as confirmed by precision rheology studies of ethylene/hex-1-ene copolymers. The complex Ti2, derivative of 5-methyl-5,10-dihydroindeno[1,2-b]indole, demonstrated the best set of properties.

Synthesis of Half-Titanocene Complexes Containing π,π-Stacked Aryloxide Ligands, and Their Use as Catalysts for Ethylene (Co)polymerizations.

A family of half-titanocene complexes bearing π,π-stacked aryloxide ligands and their catalytic performances towards ethylene homo-/co- polymerizations were disclosed herein. All the complexes were well characterized, and the intermolecular π,π-stacking interactions could be clearly identified from single crystal X-ray analysis, in which a stronger interaction could be reflected for aryloxides bearing bigger π-systems, e.g., pyrenoxide. Due to the formation of such interactions, these complexes were able to highly catalyze the ethylene homopolymerizations and copolymerization with 1-hexene comonomer, even without any additiveson the aryloxide group, which showed striking contrast to other half-titanocene analogues, implying the positive influence of π,π-stacking interaction in enhancing the catalytic performances of the corresponding catalysts. Moreover, it was found that addition of external pyrene molecules was capable of boosting the catalytic efficiency significantly, due to the formation of a stronger π,π-stacking interaction between the complexes and pyrene molecules.