Catalytic Ethylene Polymerization Research Articles

Et3Al and Et2Zn cooperatively enhanced Ti catalyzed ethylene coordinative chain transfer polymerization

Developing olefin polymerization catalytic systems for both high activity and high chain transfer efficiency by using coordinative chain transfer polymerization (CCTP) is critical for the controlled synthesis of various novel high-value polyolefin materials. While the limited choice of chain transfer agents (CTAs) makes it a challenge to achieve highly efficient CCTP as well as chain propagation due to their competition during the polymerization. Here we report using the combination of R3Al and R2Zn in equal amount for tetradentate amine-bis(phenolate) Ti complex and tridentate ketoiminate Ti complex catalyzed ethylene polymerization and observed significantly enhanced CCTP catalytic performance in terms of activity, chains/cat, fill ratio, and kct/kp vs. using R3Al as CTA. The role of R3Al and R2Zn during ethylene polymerization were probed by preliminary control experiments studies and a possible mechanistic scenario was proposed.

Ethylene Polymerization over Metal-Organic Framework-Supported Zirconocene Complexes.

Metallocene immobilization onto a solid support helps to overcome the drawbacks of homogeneous metallocene complexes in the catalytic olefin polymerization. In this study, valuable insights have been obtained into the effects of pore size, linker composition, and surface groups of metal-organic frameworks (MOFs) on their role as support materials for metallocene-based ethylene polymerization catalysis. Three distinct Zn-based metal-organic frameworks (MOFs), namely, MOF-5, IRMOF-3, and ZIF-8, with different linkers have been activated with methylaluminoxane (MAO) and zirconocene complexes, followed by materials characterization and testing for ethylene polymerization. Characterization has been performed by multiple analytical tools, including X-ray diffraction (XRD), scanning electron microscopy (SEM), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and CO Fourier transform infrared (FT-IR) spectroscopy. It was found that the interactions between MOFs, MAO, and the zirconocene complex not only lead to both catalyst activation and deactivation but also result in the creation of multiple active sites. By alteration of the MOF support, it is possible to obtain polyethylene with different properties. Notably, ultrahigh molecular weight polyethylene (UHMWPE, M W = 5.34 × 106) was obtained using IRMOF-3 as support. This study reveals the potential of MOF materials as tunable porous supports for metallocene catalysts active in ethylene polymerization.

Preparation of polyethylene/Siloxene nanocomposites through siloxene‐MgCl supported Ziegler‐Natta catalyst

AbstractThe two‐dimensional (2D) inorganic fillers could significantly improve the properties of polyolefin, thereby satisfying a wider range of applications. Herein, in this research, high‐performance polyethylene (PE)/siloxene nanocomposites were prepared through an in‐situ polymerization with layered siloxene‐supported Ti‐based catalyst. The catalytic ethylene polymerization activity of the siloxene‐supported Ziegler‐Natta catalyst was almost twice that of the MgCl2/TiCl4 catalyst when equal weights of catalysts were used. During the in‐situ polymerization, the layered siloxene fillers exhibited uniform dispersion within the PE matrix. The incorporation of a minimal amount of siloxene filler resulted in a notable enhancement in the thermal stability and mechanical properties of PE. The breaking strength, modulus, elongation at break, and Td5% of PE/siloxene nanocomposites with only 0.71 wt% siloxene were increased by 115.7%, 45.6%, 50.6%, and 58.2°C, respectively. Therefore, this research presents a straightforward method for manufacturing PE with outstanding performance.Highlights PE/siloxene nanocomposites were prepared through in‐situ polymerization. Siloxene is uniformly scattered in the PE matrix. The siloxene and matrix exhibit excellent interfacial adhesion. PE/siloxene nanocomposites with excellent properties were obtained.

Positional heterogenization effect in salicylaldimine nickel catalyzed ethylene polymerization

Positional heterogenization effect in salicylaldimine nickel catalyzed ethylene polymerization

Non-Symmetrically Fused Bis(arylimino)pyridines with para-Phenyl Substitution: Exploring Their Use as N′,N,N″-Supports in Iron Ethylene Polymerization Catalysis

Through the implementation of a one-pot strategy, five examples of non-symmetrical [N,N-diaryl-11-phenyl-1,2,3,7,8,9,10-heptahydrocyclohepta[b]quinoline-4,6-diimine]iron(II) chloride complexes (aryl = 2,6-Me2Ph Fe1, 2,6-Et2Ph Fe2, 2,6-i-Pr2Ph Fe3, 2,4,6-Me3Ph Fe4, and 2,6-Et2-4-MePh Fe5), incorporating fused six- and seven-membered carbocyclic rings and appended with a remote para-phenyl group, were readily prepared. The molecular structures of Fe2 and Fe3 emphasize the variation in fused ring size and the skewed disposition of the para-phenyl group present in the N′,N,N″-ligand support. Upon activation with MAO or MMAO, Fe1–Fe5 all showed high catalytic activity for ethylene polymerization, with an exceptional level of 35.92 × 106 g (PE) mol−1 (Fe) h−1 seen for mesityl-substituted Fe4/MMAO operating at 60 °C. All catalysts generated highly linear polyethylene with good control of the polymer molecular weight achievable via straightforward manipulation of run temperature. Typically, low molecular weight polymers with narrow dispersity (Mw/Mn = 1.5) were produced at 80 °C (MMAO: 3.7 kg mol−1 and MAO: 4.9 kg mol−1), while at temperatures between 40 °C and 50 °C, moderate molecular weight polymers were obtained (MMAO: 35.6–51.6 kg mol−1 and MAO: 72.4–95.5 kg mol−1). Moreover, analysis of these polyethylenes by 1H and 13C NMR spectroscopy highlighted the role played by both β-H elimination and chain transfer to aluminum during chain termination, with the highest rate of β-H elimination seen at 60 °C for the MMAO-activated system and 70 °C for the MAO system.

Dearomatized diimines for nickel(ii) and palladium(ii) catalyzed ethylene polymerization and copolymerization

Dual steric enhancement was achieved through the combination of a dearomatized acenaphthyl backbone and bulky ortho substituents. The role of this bulky backbone in metal-catalyzed ethylene (co)polymerization was investigated.

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.

Origin of Suppressed Chain Transfer in Phosphinephenolato Ni(II)-Catalyzed Ethylene Polymerization.

Recent breakthroughs in the generation of polar-functionalized and more sustainable degradable polyethylenes have been enabled by advanced phosphinephenolato Ni(II) catalysts. A key has been to overcome this type of catalysts' propensity for extensive chain transfer to enable formation of high-molecular-weight polyethylene chains. We elucidate the mechanistic origin of this paradigm shift by a combined experimental and theoretical study. Single-crystal X-ray structural analysis and cyclic voltammetry of a set of six different catalysts with variable electronics and sterics, combined with extensive pressure reactor polymerization studies, suggest that an attractive Ni-aryl interaction of a P-[2-(aryl)phenyl] is responsible for the suppression of chain transfer. This differs from the established picture of steric shielding found for other prominent late transition metal catalysts. Extensive density functional theory studies identify the relevant pathways of chain growth and chain transfer and show how this attractive interaction suppresses chain transfer.

DFT insight into metals and ligands substitution effects on reactivity of phenoxy-imine catalysts for ethylene polymerization

The reaction mechanism of ethylene (ET) polymerization catalyzed by the phenoxy-imine (FI) ligands using DFT calculations was studied. Among five possible isomers, isomer A which has an octahedral geometry and a (cis-N/trans-O/cis-Cl) arrangement is the most stable pre-reaction Ti-FI dichloride complex. The isomer A can be activated by MAO to form the active catalyst and the active form was used for the study of the mechanism for Ti-FI. The second ethylene insertion was found to be the rate-determining step of the catalyzed ethylene polymerization. To examine the effect of group IVB transition metals (M = Ti, Zr, Hf) substitutions, calculated activation energies at the rate-determining step (EaRDS) were compared, where values of EaRDS of Zr < Hf < Ti agree with experiments. Moreover, we examined the effect of substitution on (O, X) ligands of the Ti-phenoxy-imine (Ti-1) based catalyst. The results revealed that EaRDS of (O, N) > (O, O) > (O, P) > O, S). Hence, the (O, S) ligand has the highest potential to improve the catalytic activity of the Ti-FI catalyst. We also found the activation energy to be related to the Ti-X distance. In addition, a novel Ni-based FI catalyst was investigated. The results indicated that the nickel (II) complex based on the phenoxy-imine (O, N) ligand in the square-planar geometry is more active than in the octahedral geometry. This work provides fundamental insights into the reaction mechanism of M − FI catalysts which can be used for the design and development of M − FI catalysts for ET polymerization.

A “Catalyst+Support” Strategy for Salicylaldimine Nickel Catalyzed Ethylene Polymerization and Copolymerization with Polar Monomers

A “Catalyst+Support” Strategy for Salicylaldimine Nickel Catalyzed Ethylene Polymerization and Copolymerization with Polar Monomers

New Ni(II)-Ni(II) Dinuclear Complex, a Resting State of the (α-diimine)NiBr2/AlMe3 Catalyst System for Ethylene Polymerization

A novel room-temperature stable diamagnetic nickel complex 2 was detected upon activation of Brookhart-type ethylene polymerization pre-catalyst LNiBr2 (1, L = 1,4-bis-2,4,6-trimethylphenyl-2,3-dimethyl-1,4-diazabuta-1,3-diene) with AlMe3. Using in situ 1H, 2H, and 13C NMR spectroscopy, as well as DFT calculations, this species has been identified as an antiferromagnetically coupled homodinuclear complex [LNiII(μ-Me)(μ-CH2)NiIIL]+Br−. Its behavior in the reaction solution is characteristic of the resting state of nickel catalyzed ethylene polymerization.

Lewis acid modulation in phosphorus phenol nickel catalyzed ethylene polymerization and copolymerization

A series of phosphorus phenol nickel catalysts containing N atoms were designed and synthesized, which can be coordinated with a metal salt Lewis acid to improve the steric hindrance of the catalyst and enhance the performance of the catalyst.

Ti-iminocarboxylate catalyzed polymerization of ethylene to highly crystalline, disentangled, ultrahigh molecular weight polyethylene

Disentangled ultrahigh molecular weight polyethylene (d-UHMWPE) is a niche, highly sought-after, and an emerging class of polyethylene. However, the synthesis of d-UHMWPE is uncommon and is equally challenging. Here, we report a Ti-iminocarboxylate complex that produces d-UHMWPE under ambient polymerization conditions. Treatment of tetrakis(dimethylamido-titanium) [Ti(NMe2)4] with 2-((4-methoxybenylidene)amino)benzoic acid produced a novel titanium complex Cat.1 [bis-dimethylamido-Ti-(bis-iminocarboxylate)]. The identity of Cat.1 was unambiguously ascertained using a combination of 1-2D NMR spectroscopy and mass analysis. Cat.1 was activated using various cocatalysts, and MMAO (modified methylaluminoxane) outperformed the others. Screening of polymerization parameters suggested an Al/Ti ratio of 1000, 4 bar ethylene pressure, 35 °C temperature, and a polymerization time of 30 min as the optimal condition. Under the optimized polymerization conditions, Cat.1 polymerizes ethylene to ultrahigh molecular weight polyethylene with a weight average molecular weight (Mw) of 2.5 × 106 g/mol. The thermal behavior of the thus prepared material disclosed a highly crystalline [crystallinity χ (DSC) 96 %], strictly linear polyethylene. Detailed thermal analysis of the nascent polyethylene using a specifically designed DSC method revealed the existence of a high melting peak at 139–140 °C, which is a hallmark of disentangled UHMWPE. Thus, a homogeneous, single-site ethylene polymerization catalyst has been developed, which upon activation with MMAO produced highly crystalline d-UHMWPE.

Comparative Investigation of η6-Arene Tethered Ru(II) Complexes with Different Tethered Heteroatoms for Ethylene Polymerization Catalysis: Experimental and DFT Studies

Comparative Investigation of η⁶-Arene Tethered Ru(II) Complexes with Different Tethered Heteroatoms for Ethylene Polymerization Catalysis: Experimental and DFT Studies

Cocatalyst effects in α-diimine nickel catalyzed ethylene polymerization

Two α-diimine nickel dimethyl complexes bearing substituents with different steric hindrance effects were synthesized and characterized. In the absence of any organoaluminium cocatalysts or scavengers, commercially available organoboron cocatalysts B(C6F5)3 (B1) or [Ph3C][B(C6F5)4] (B2), can activate these α-diimine nickel dimethyl complexes to catalyze ethylene polymerization. Compared with B2, cocatalyst B1 led to significantly increased catalytic activities, resulting in polyethylenes with slightly lower molecular weight, higher branching densities and lower melting temperatures. Furthermore, the resulting polyolefin materials exhibited good tensile and elastic properties. Density functional theory (DFT) calculations indicated that the counter anion derived from B1 can form a secondary interaction with the Ni center in the active species, which may contribute to the increased stability and activity.

Cocatalyst Effect in Transition Metal Catalyzed Ethylene Polymerization and Copolymerization

AbstractTransition‐metal‐based olefin polymerization catalysts usually require activation with a cocatalyst to initiate polymerization reactions. Borane type cocatalyst is one of the most important classes of cocatalysts that can significantly influence the catalytic performances. In this contribution, we designed and prepared a series of borane cocatalysts, and subsequently investigated their properties in a titanium‐based Constrained Geometry Catalyst (CGC‐Ti) catalyzed ethylene polymerization and ethylene/1‐octene copolymerization. Among these borane cocatalysts, B(C6F5)2OtBu exhibited outstanding cocatalyst performances, achieving activity of up to 1.06×107 g mol−1 h−1 and polymer molecular weight of up to 88.2×104 g mol−1 in ethylene polymerization. In ethylene/1‐octene copolymerization, this borane enabled activity of up to 2.46×106 g mol−1 h−1, affording copolymers with comonomer incorporation of up to 12.8 % and copolymer molecular weight up to 18.3×104 g mol−1. The superior properties of B(C6F5)2OtBu originated from its unique activation mode with the oxygen atom being coordinated to the active metal center.

Lewis acids modulation in phosphine‐sulfonate palladium catalyzed ethylene polymerization

Lewis acid modulation in metal‐catalyzed olefin polymerization have received increasing attention. In this work, a series of N‐containing phosphine‐sulfonate palladium complexes were synthesized, characterized and used as stimuli‐responsive type catalysts. The introduction of metal Lewis acids results in significantly improved catalytic performances of N‐containing phosphine‐sulfonate Pd catalysts in ethylene polymerization, resulting in improved catalytic activities and high‐molecular‐weight polyethylenes (Mn up to 369.2 kg mol−1). It was indicated that the metal Lewis acids can form interactions with the N‐containing moieties on the phosphine‐sulfonate Pd catalysts. This provides a simple and versatile strategy to tune the properties of olefin polymerization catalysts.

Density functional theory and CCSD(T) evaluation of ionization potentials, redox potentials, and bond energies related to zirconocene polymerization catalysts.

Quantum-mechanical-based computational design of molecular catalysts requires accurate and fast electronic structure calculations to determine and predict properties of transition-metal complexes. For Zr-based molecular complexes related to polyethylene catalysis, previous evaluation of density functional theory (DFT) and wavefunction methods only examined oxides and halides or select reaction barrier heights. In this work, we evaluate the performance of DFT against experimental redox potentials and bond dissociation enthalpies (BDEs) for zirconocene complexes directly relevant to ethylene polymerization catalysis. We also examined the ability of DFT to compute the fourth atomic ionization potential of zirconium and the effect the basis set selection has on the ionization potential computed with CCSD(T). Generally, the atomic ionization potential and redox potentials are very well reproduced by DFT, but we discovered relatively large deviations of DFT-calculated BDEs compared to experiment. However, evaluation of BDEs with CCSD(T) suggests that experimental values should be revisited, and our CCSD(T) values should be taken as most accurate.

Dynamic Modeling of Industrial Loop Reactors for Catalytic Ethylene (Co)polymerization: Pressure Safety Valves

AbstractIn industrial loop reactors, for catalytic ethylene (co)polymerization, the heat produced by polymerization can result in temperature and pressure increase, which in turn can lead to reactor breakage, explosion, and consequent release of toxic/flammable fluids in the environment. To predict the reactor temperature and pressure during ethylene (co)polymerization and assess the performance of presure safety valves (PSVs) in response to emergency accidents, an integrated mathematical approach is followed including catalyst kinetics, thermodynamics, and transport properties modeling. A catalytic ethylene (co)polymerization kinetic model is used to predict the catalyst activity variation with respect to reactor temperature and the heat produced by the polymerization reaction during a reaction runaway. The Sanchez–Lacombe equation of state (SL EOS) is utilized in order to predict the reactor pressure for different slurry mixture compositions and the slurry densities at different temperatures, pressures and solids weight fractions. Dynamic macroscopic mass and energy balances are derived to calculate the dynamic evolution of concentrations of the various molecular species as well as the temperature changes in the loop reactor. The model can predict the temperature and pressure increase rates and the maximum flow rate at the PSVs during the runaway.

First example of cationic titanium (III) complexes with crown ether as catalysts for ethylene polymerization

Complex cations with a vacant coordination site are considered as the most plausible catalytically active centers of metallocene and post-metallocene polymerization catalysts. For the first time we demonstrated that cationic titanium (III) complexes stabilized with crown ether can be used as pre-catalysts for ethylene polymerization. In the presence of alkyl aluminum chlorides and MgBu2 as cocatalysts, these complexes catalyze ethylene polymerization to produce Ultra High Molecular Weight Polyethylene (UHMWPE) with productivity up to 4650 kgPE/mol Ti h⋅atm and molecular weight up to 1.8·106 Da. UHMWPE powders were processed by the solid-phase method with subsequent orientation drawing into high-strength (1.4–2.1 GPa) and high-modulus (91–118 GPa) films.