Olefin Polymerization Research Articles

Late Transition Metal Olefin Polymerization Catalysts Derived from 8-Arylnaphthylamines

Late transition metal catalysts represent a significant class of olefin polymerization catalysts that have played an essential role in advancing the polyolefin industry owing to their highly tunable ligands and low oxophilicity. A key feature for the design of late transition metal catalysts lies in the steric bulk of the o-aryl substituents. Bulky 8-arylnaphthylamines have emerged as a promising aniline candidate for conducting high-performance catalysts by introducing axially steric hindrance around the metal center. This review focuses on late transition metal (Ni, Pd, Fe) catalysts derived from 8-arylnaphthylamines, surveying their synthesis, structural features, and catalytic applications in olefin (co)polymerizations. Additionally, the relationship between catalyst structure and catalytic performance is discussed, highlighting how these unique ligand systems influence polymerization activity, molecular weight, and polymer branching.

Correlating Heterogeneities in Support Fragmentation to Polymer Morphology in Metallocene‐Based Propylene Polymerization Catalysis

In the field of olefin polymerization catalysis, metallocenes are heterogenized with methylaluminoxane onto silica supports to yield active catalysts. During olefin polymerization, these silica supports act as a framework to control the fragmentation stage, thereby influencing the final polymer product and preventing reactor fouling and fines formation. This study investigates the influence of different silica supports induced on the final polymer product. To study a broad range of silica supports from an industrial silica database, we utilize a hierarchical clustering method to cluster the supports based on their physical properties. From the clustering method, five supports representing the clusters and an industrial benchmark were analyzed at different polymerization stages using Focused Ion Beam Scanning Electron Microscopy (FIB‐SEM) and Micro‐computed Tomography (MicroCT). This combined FIB‐SEM/MicroCT methodology revealed differences in both fragmentation behavior and polymer morphologies based on structural features, including macropores, mesopores, spray‐dried shells, spray‐dried spheres, and denser shells. The heterogeneity and ideal fragmentation behavior was further assessed by calculating the replication factor of each support, indicating that silica materials containing macropores and spray‐dried shells have an almost ideal replication phenomenon. This multi‐scale analysis revealed new understanding of catalyst fragmentation for different supports.

Hydrazine‐Catalysed Ring‐Opening Metathesis Polymerization Of Cyclobutenes

AbstractMaterials formed by the ring‐opening metathesis polymerization (ROMP) of cyclic olefins are highly valued for industrial and academic applications but are difficult to prepare free of metal contaminants. Here we describe a highly efficient metal‐free ROMP of cyclobutenes using hydrazine catalysis. Reactions can be initiated via in situ condensation of a [2.2.2]‐bicyclic hydrazine catalyst with an aliphatic or aromatic aldehyde initiator. The polymerizations show living characteristics, achieving excellent control over molecular weight, low dispersity values, and high chain‐end fidelity. Additionally, the hydrazine can be used in substoichiometric amounts relative to the aldehyde chain‐end while maintaining good control over molecular weight and low dispersity values, indicating that a highly efficient chain transfer mechanism is occurring.

Radical Isomerization Homopolymerization of Linear α‐Olefins to Access C5, C6 or C7 Polymers

AbstractNon‐activated linear α‐olefins are valuable building blocks for organic transformation or olefin (co)polymerization, but they are recognized as textbook knowledge for non‐homopolymerizable monomers under radical conditions. In this article, we disclose our effort to achieve an unprecedented library of all carbon‐bonded sequence‐regulated polymers via radical isomerization homopolymerization of α‐olefin derivatives. The success of this distinctive polymerization is attributed to the remarkable efficiency and selectivity exhibited during the cyano group migration or hydrogen atom transfer, which is greatly enhanced by the precise engineering of their monomer structures. This polymerization process enables the elongation of polymer chains by five, six, or seven carbon atoms at each propagation step. These polymers, obtained through the cyano group migration or hydrogen atom transfer involved radical isomerization polymerization processes, emerge as promising candidates resembling polyethylene or polyacrylonitrile copolymers.

Radical Isomerization Homopolymerization of Linear α-Olefins to Access C5, C6 or C7 Polymers.

Non-activated linear α-olefins are valuable building blocks for organic transformation or olefin (co)polymerization, but they are recognized as textbook knowledge for non-homopolymerizable monomers under radical conditions. In this article, we disclose our effort to achieve an unprecedented library of all carbon-bonded sequence-regulated polymers via radical isomerization homopolymerization of α-olefin derivatives. The success of this distinctive polymerization is attributed to the remarkable efficiency and selectivity exhibited during the cyano group migration or hydrogen atom transfer, which is greatly enhanced by the precise engineering of their monomer structures. This polymerization process enables the elongation of polymer chains by five, six, or seven carbon atoms at each propagation step. These polymers, obtained through the cyano group migration or hydrogen atom transfer involved radical isomerization polymerization processes, emerge as promising candidates resembling polyethylene or polyacrylonitrile copolymers.

Development of Group IV Metal Complexes Bearing Thioether-Amido Ligands with Enhanced High-Temperature Catalytic Performance toward Olefin Copolymerization.

The development of homogeneous metal catalysts with both high activity and exceptional thermal stability is crucial for the efficient synthesis of polyolefin elastomers (POEs) through solution-phase olefin polymerization. In this study, a series of Hf (Hf1-Hf5), Zr (Zr1), and Ti (Ti1) complexes featuring thioether-amido ligands were synthesized and carefully characterized using advanced techniques such as 1H and 13C NMR spectroscopy as well as single-crystal X-ray diffraction analysis for Hf4 and Hf5. The results revealed that the catalytic activity and 1-octene incorporation efficiency of these metal complexes followed the trend Hf > Zr > Ti, underscoring the significant impact of the metal center on catalytic performance. Furthermore, the choice of ligands was found to play a critical role in dictating the catalytic properties, with ligands bearing less steric hindrance on the sulfur atom proving to be more favorable for copolymerization reactions. Notably, the Hf complex Hf1, featuring a methyl group on the sulfur atom, displayed exceptional catalytic activity as high as 21,060 kg(polymer)·mol-1(Hf)·h-1 toward ethylene/1-octene copolymerization at 120 °C and produced POE with a high molecular weight (Mw = 6.3 × 104 g·mol-1), relatively narrow distribution (Đ = 2.4), and high incorporation of 1-octene (34.1 mol %). This study demonstrates the potential of tailored ligand design in developing efficient metal catalysts for the production of high-value-added POEs.

Degradable polyolefins prepared by integration of disulfides into metathesis polymerizations with 3,6-dihydro-1,2-dithiine.

Disulfide-containing polyolefins were synthesized by ring-opening metathesis polymerization (ROMP) of the 6-membered disulfide-containing cyclic olefin, 3,6-dihydro-1,2-dithiine, which was prepared by ring-closing metathesis of diallyl disulfide. This approach facilitated the production of disulfide-containing unsaturated polyolefins as copolymers with disulfide monomer units embedded within a poly(cyclooctene) or poly(norbornene) framework. The incorporation of disulfides into the polymer backbone imparts redox responsiveness and enables polymer degradation via chemical reduction or thiol-disulfide exchange. This ROMP copolymerization strategy yielded both linear polyolefins, as well as bottlebrush polymers, with degradable segments, thereby broadening the scope of responsive polymer architectures synthesized by ROMP.

Benchtop-Stable Carbyl Iminopyridyl NiII Complexes for Olefin Polymerization.

Design of catalysts for Ni-catalyzed olefin polymerization predominantly focuses on ligand design rather than the activation process when attempting to achieve a broader scope of polyolefin micro- and macrostructures. Air-stable alkyl-or aryl-functionalized NiII precatalysts were designed which eliminate the need of in situ alkylating processes and are activated solely by halide abstraction to generate the cationic complex for olefin polymerization. These complexes represent an emerging class of olefin polymerization catalysts, enabling the study of various cocatalysts forming either inner- or outer-sphere ion pairs. It is demonstrated that an organoboron cocatalyst activation produces a well-defined ion pair, which in contrast to ill-defined organoaluminum cocatalysts, can directly activate the complex by halide abstraction to yield comparatively higher molecular weight homo/copolymers. Under high ethylene pressure, broader branching densities and the gradual incorporation of short-chain branches were achieved, circumventing the need for elaborate ligand design and copolymerization with α-olefins. The underlying chain-walking mechanism and ion pair interactions were further elucidated by DFT calculations. A phenyl group on the bridging carbon functioned as a rotational barrier, producing higher molecular weight polymers compared to methyl-substituted analogs. Here, we provide a perspective to manipulate the iminopyridyl NiII system, leveraging ion pair interactions and ligand design to govern polyolefin molecular weights and microstructures.

Rational Design of Cyclopentadiene-Based Super- and Hyperacids Based on Aromaticity.

The design and synthesis of neutral organic superacids have been of interest recently due to their vast applications in chemistry and material sciences, for example, olefinic polymerization, isolation of highly reactive short-lived cations, etc. Cyclopentadiene behaves as a mild organic acid, producing a stable conjugate base by gaining aromaticity and conjugation after deprotonation. To stabilize conjugate bases of organic acids to show superacidities and hyperacidities, we considered aromatic phenyl substituents with cyclopentadiene (mono-, di-, and triphenyl-substituted cyclopentadiene and their cyano derivatives). The MP2, DFT (B3LYP, M06-2X), and CBS-QB3 methods were used to calculate the gas-phase proton affinities of the parent cyclopentadiene, and the DFT methods were chosen for the substituted cyclopentadiene as they yield an experimental proton affinity of cyclopentadiene of 253.66 kcal/mol (Expt. 253.6 ± 1.3 kcal/mol). The stable trisubstituted cyclopentadiene derivative shows gas-phase enthalpies of deprotonation (ΔHacid) of 245 and 239 kcal/mol with DFT B3LYP and M06-2X methods, respectively, with values in the range of hyperacidity. Some of the tautomers of cyclopentadiene derivatives show hyperacidity, with proton affinity values of 205-240 kcal/mol. Triphenyl-substituted cyclopentadiene behaves as a moderate acid but transforms into a superacid after replacing the phenyl group with nitrobenzene, which is a stronger acid than H2SO4 (ΔHacid = 298 kcal/mol). The nucleus-independent chemical shift (NICS) shows the extent of conjugation in the derivatives of cyclopentadienyl anions after deprotonation, which affects the stabilities of conjugate bases, i.e., the acidities of the protonated species. The calculated harmonic oscillator model of aromaticity and NICS indices reveal that the stability of conjugate bases as well as their acidities increase with increasing aromaticity of cyclopentadiene rings after deprotonation in all molecules.

Hydrazine-Catalysed Ring-Opening Metathesis Polymerization Of Cyclobutenes.

Materials formed by the ring-opening metathesis polymerization (ROMP) of cyclic olefins are highly valued for industrial and academic applications but are difficult to prepare free of metal contaminants. Here we describe a highly efficient metal-free ROMP of cyclobutenes using hydrazine catalysis. Reactions can be initiated via in situ condensation of a [2.2.2]-bicyclic hydrazine catalyst with an aliphatic or aromatic aldehyde initiator. The polymerizations show living characteristics, achieving excellent control over molecular weight, low dispersity values, and high chain-end fidelity. Additionally, the hydrazine can be used in substoichiometric amounts relative to the aldehyde chain-end while maintaining good control over molecular weight and low dispersity values, indicating that a highly efficient chain transfer mechanism is occurring.

Atomic Layer Deposition of γ‐Al2O3 on Hexagonal Boron Nitride: A Hybrid Support for Metallocene Catalysts

AbstractHexagonal boron nitride (hBN), also known as white graphene, has recently gained larger attention due to its unique physical and chemical properties. Owing to its excellent thermal conductivity and stability, hBN has been reported as an effective filler in many polymers. This study explores the potential of hBN as a catalyst support and filler for olefin polymerization. We report the atomic layer deposition (ALD) of γ‐Al2O3 on hydroxyl‐functionalized hBN. The alumina precursor, methylaluminoxane, showed high selectivity, depositing Al species only on the B‐OH sites, while B−O‐O−B sites remained unreacted. The hBN/γ‐Al2O3 hybrid was characterized by Fourier transform infrared (FTIR) spectroscopy, X‐Ray diffraction and transmission electron microscopy (TEM). The deposition of the aluminum over the hBN sheets was confirmed. The hBN/γ‐Al2O3 was used as a support for metallocene catalysts. The supported catalyst complex was highly active and produced ethylene‐propylene polymers with molecular weights up to 10 times higher, as demonstrated by gel permeation chromatography (GPC)

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.

Rare-Earth Metallocenes for Polymerization of Olefins and Conjugated Dienes: From Fundamental Studies to Olefin Block Copolymers.

The various steps in the mechanism of olefin polymerizations mediated by neutral rare-earth metallocene complexes are discussed. The complexes are either trivalent hydride and alkyl rare-earth compounds or divalent metallocenes that are activated by the monomer via an oxidation step. The stereospecific polymerizations of conjugated dienes based on the association of a cationic metallocene complex and an alkylaluminum and the polymerization mechanism based on monomer insertion into an aluminum-carbon bond are also discussed. The exploitation of metallocene complexes for the copolymerization of olefins with conjugated dienes is the subject of a third part of this review. The synthesis of new elastomers called ethylene butadiene rubber (EBR) is highlighted. Finally, the use of rare-earth metallocenes in macromolecular engineering is detailed. This includes the synthesis of functional polyolefins and block copolymers including thermoplastic elastomers.

Group 4 Complexes Supported by Pyridine-2-Phenolate-6-Arylmethine Ligands: Spectroscopic and Structural Characterization and Olefin Polymerization Catalysis

Group 4 Complexes Supported by Pyridine-2-Phenolate-6-Arylmethine Ligands: Spectroscopic and Structural Characterization and Olefin Polymerization Catalysis

Structure of methylaluminoxane (MAO): Extractable [Al(CH 3 ) 2 ] + for precatalyst activation

Methylaluminoxane (MAO) is used as a precatalyst activator for million ton–scale production of commercial polyolefins, but its precise structure and associated activation mechanisms have been a fundamental research puzzle for more than 40 years. We report here the crystallographic characterization of an active MAO component, which reveals a discrete two-dimensional sheet cluster [Al 33 O 26 (CH 3 ) 47 ][Al(CH 3 ) 3 ] 2 featuring two trimethylaluminum units, Al(CH 3 ) 3 , coordinated to two unsaturated aluminum sites. Our structural data are consistent with the hypothesis that the active sites bear coordinated Al(CH 3 ) 3 and provide [Al(CH 3 ) 2 ] + for precatalyst activation. Quantum chemical calculations revealed the most preferred sites for [Al(CH 3 ) 2 ] + abstraction (a change in Gibbs free energy of 0.0 kilocalories per mole). Olefin polymerization tests on metallocenes activated with the crystallized MAO show higher activities than with the commercial MAO.

Atomistic Simulation of Hf-Pyridyl Amido-Catalyzed Chain Transfer Alkene Polymerization Reaction and Its Machine Learning for Extraction of Essential Descriptors: Effect of Microscopic Steric Hindrance on the Monomer Insertion Process.

The microscopic effects of each substituent of the Hf catalyst and the growing polymer on the monomer insertion process were investigated for Hf-pyridyl amido-catalyzed coordinative chain transfer polymerization using the Red Moon method. Since the Hf catalyst has two reaction sites, cis- and trans-sites, we separately applied the appropriate analysis methods to each one, revealing that the naphthalene ring influenced monomer insertion at the cis-one, while the i-Pr group and the hexyl group of the adjacent 1-octene unit did the trans-one. It was interesting to find that the hexyl group of the 1-octene-inserted catalyst (oHfCat) pushes the naphthalene ring toward the cis-site and narrows the space at the cis-site, thus indirectly creating a steric hindrance to cis-insertions. Further, the relative position of the Hf catalyst and the growing polymer was found to be strongly influenced by the patterns of insertion reactions, i.e., cis- or trans-insertions. In particular, it was clarified that, after trans-insertions, the growing polymer on the Hf atom covers the cis-site, making cis-insertion less likely to occur. These studies reveal the microscopic effects of the catalyst substituents and the growing polymer on the catalyst during the polymerization reaction process; these microscopic analyses using the RM method should provide atomistic insights that are not easy to obtain experimentally for advanced catalyst design and polymerization control.

Ammonium Tetrakis(pentafluorophenyl)borate: Preparation and Application in Olefin Coordination Polymerization as the Cocatalyst Compound.

Metallocene catalysts have attracted much attention from academia and industry for their excellent catalytic activity in the field of olefin polymerization. Cocatalysts play a key role in metallocene catalytic systems, which can not only affect the overall catalytic activity, but also have an obvious influence on the structure and properties of the polymer. Although methylaluminoxane (MAO) is currently the most widely used cocatalyst, its price increases the production cost of polyolefin materials. Ammonium tetrakis(pentafluorophenyl)borate has shown excellent performance in polymerization, being one of the best substitutes for the traditional cocatalyst MAO. Compared with the main catalyst, whose composition and structure are relatively complex, the research on cocatalyst is very limited. This review mainly introduces the research history, preparation methods, and application progress in polymerization of ammonium tetrakis(pentafluorophenyl)borate, deepening our understanding of the role of cocatalyst in polymerization, with the hope of inspiring brand-new thinking on improving and enhancing the overall performance of catalyst systems.

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.

Alkene Polymerization with Catalysts Containing Ionic Complexes [2L·M@dibenzo-18-crown-6]+[TiCl5·L]– (L = CH3CN, M = Li+, K+)

Alkene Polymerization with Catalysts Containing Ionic Complexes [2L·M@dibenzo-18-crown-6]+[TiCl5·L]– (L = CH3CN, M = Li+, K+)

Ethylene Polymerizations Catalyzed by Fluorinated "Sandwich" Diimine-Nickel and Palladium Complexes.

Nickel and palladium complexes bearing "sandwich" diimine ligands with perfluorinated aryl caps have been synthesized, characterized, and explored in ethylene polymerization reactions. The X-ray crystallographic analysis of the precatalysts 16 and 6b shows differences from their nonfluorinated analogues 17 and 19, with the perfluorinated aryl caps centered precisely over the nickel and palladium centers, which results in higher buried volumes of the metal centers relative to the nonfluorinated analogues. The sandwich diimine-palladium complexes 5a and 5b containing perfluorinated aryl caps polymerize ethylene in a controlled fashion with activities that are substantially increased compared with their nonfluorinated analogues. Migratory insertion rates in relevant methyl ethylene complexes agree with the activities exhibited in bulk polymerization experiments. DFT studies suggest that facility of ethylene rotation from its preferred orientation perpendicular to the Pd-alkyl bond into a parallel in-plane conformation contributes to the higher polymerization activity for 5b relative to 18a. For these palladium systems, polymer molecular weights can be controlled via hydrogen addition (hydrogenolysis), which is unusual for late-transition-metal-catalyzed olefin polymerizations with no catalyst deactivation occurring. Sandwich diimine-nickel complexes 6a and 6b with perfluorinated aryl caps show ethylene polymerization activities that are about half of those of classical tetraisopropyl-substituted catalyst 2 but again are more active than the analogous nonfluorinated sandwich complexes. Ethylene polymerizations exhibit living behavior, and branched ultrahigh-molecular-weight polyethylenes (UHMWPEs) with very low-molecular-weight distributions (less than 1.1) are obtained. The activated nickel catalysts are stable in the absence of monomer and show good long-term stability at 25 °C.