Poly Methyl Research Articles

Karl Ziegler - Early Career of a Scientist.

Karl Ziegler is considered one of the most outstanding chemists of the 20th century. In particular, his work on organometallic mixed catalysts, which allows the polymerization of ethylene at normal pressure, led to a revolution in plastics production and changed the everyday life of all mankind. In 1963, he was awarded the Nobel Prize in Chemistry for this work, together with Giulio Natta. This article focuses on Ziegler's early career, which has received little attention to date. It describes his youth and study years in Marburg, which partly coincide with the First World War. Subsequently, his postdoctoral period is examined, which led him via Marburg and Frankfurt to his first associate professorship in Heidelberg. Special attention is paid to his relationship to National Socialism, which he opposed. As a result, Ziegler experienced professional difficulties in the 1930s, such as repeated rejection when filling various professorships. His appointment as a full professor in Halle and his subsequent directorship at the Max-Planck-Institut für Kohlenforschung (Coal Research), where he finally achieved his greatest research achievement, are described in the following.

Thorium Recovery with Crown Ether–Polymer Composite Membranes

Thorium is a weak radioactive element, but the control of its concentration in natural aqueous systems is of great interest for health, because it is a toxic heavy metal. The present paper presents the recovery of thorium from diluted synthetic aqueous systems by nanofiltration. The membranes used for the nanofiltration of systems containing thorium species are composites containing 4′-Aminobenzo-15-crown-5 ether (ABCE) and sulfonated poly–etherether–ketone (sPEEK). The composite membranes (ABCE–sPEEK) were characterized by scanning electron microscopy (SEM), energy-dispersive X–Ray spectroscopy (EDAX), thermal analysis (TG and DSC), and from the perspective of thorium removal performance. To determine the process performance, the variables were the following: the nature of the composite membrane, the concentration of thorium in the aqueous systems, the rotation speed of the stirrer, and the pressure and the pH of the thorium aqueous system. When using pure water, a permeate flux value of 12 L·m−2 h−1 was obtained for the sPEEK membrane, and a permeate flux value of up to 15 L·m−2 h−1 was obtained for the ABCE–sPEEK composite membrane. The use of mechanical stirring, with a propeller stirrer, lead to an increase in the permeate flux value of pure water by about 20% for each of the studied membranes. Depending on the concentration of thorium and the pH of the feed solution, retentions between 84.9% and 98.4% were obtained. An important observation was the retention jump at pH 2 for the ABCE–sPEEK composite membrane. In the paper, a thorium ion retention mechanism is proposed for the sPEEK membrane and the ABCE–sPEEK composite membrane.

Ethylene Polymerization Activity vs Grafting Affinity Trade-off Revealed by Importance Learning Analysis of In Silico Phillips Catalyst

Ethylene Polymerization Activity vs Grafting Affinity Trade-off Revealed by Importance Learning Analysis of <i>In Silico</i> Phillips Catalyst

Adjustment of Electronic (OMe and NO2) and Steric (CHPh2) Effects in Bis(imino)pyridinyliron Precatalysts for Producing High Molecular Weight Linear PE

AbstractBased on variations in steric and electronic substituents in the N‐aryl unit, a set of five 2‐[1‐(arylimino)ethyl]‐6‐[1‐(2‐benzhydryl‐4‐nitro‐6‐methoxyphenylimino)ethyl]pyridyliron dichloride complexes (where aryl=2,6‐dimethylphenyl (Fe‐Me2), 2,6‐diethylphenyl (Fe‐Et2), 2,6‐diisopropyl (Fe‐iPr2), 2,4,6‐trimethylphenyl (Fe‐Me3), 2,6‐diethyl‐4‐methylphenyl (Fe‐Et2Me)) were synthesized and investigated for ethylene polymerization. Their structures and compositions were confirmed by FTIR, elemental analysis, and X‐ray diffraction analysis (Fe‐Et2 and Fe‐iPr2), revealing a distorted square pyramidal geometry around the iron center. When activated in situ with MAO or MMAO, these iron complexes acted as highly active precatalysts, achieving activity levels up to 29.0×106 gPE molFe−1 h−1 for a 5‐min reaction at 60 °C. A notable characteristic of these precatalysts is their high thermal stability, maintaining significant activity (2.0×106 gPE molFe−1 h−1) at temperatures up to 100 °C. Importantly, the incorporation of strong electron‐withdrawing groups in the ligand structure favored the production of polyethylene with high molecular weights (up to 407.5 kg mol−1) across various reaction conditions, surpassing those of most previously reported iron complexes. Moreover, less hindered iron precatalysts showed higher activity compared to more hindered ones. However, the trend reversed when comparing the molecular weight of obtained polyethylene: more sterically hindered precatalysts yielded higher molecular weight polymers. The molecular weight distributions ranged from monomodal to bimodal with broad dispersity. DSC thermograms and 1H/13C NMR spectra of the polyethylene confirmed its highly linear microstructure, evidenced by sharp endothermic peaks and pronounced singlets for the −(CH2)n− repeating units.

Metal-Free Photoinitiated, Controlled Cationic Polymerization of Vinyl Ethers Using Organic Iodides

Metal-Free Photoinitiated, Controlled Cationic Polymerization of Vinyl Ethers Using Organic Iodides

Molding blends of silicone polymer / polypropylene with durable resistant to extreme conditions based on migration and compatibility of molecular chains

Because of low surface energy, silicone polymers would easily peel off from polypropylene (PP) substrate as hydrophobic coatings and they are incompatible with PP in melt-blending process as well. Therefore, ethylene polymers modified with both silicone and alkane side-groups were prepared by nucleophilic substitution in this work. It was confirmed that these prepared polymers could migrate and aggregate to the surface of the blends at that melting temperature when blended with PP due to the low surface energy and high entropy of silicone side groups. Meanwhile, chain entanglement was achieved between alky side-groups of silicone polymers and polymer chain of PP by melt-blending process, so that the compatibility of the blends was improved and the bonding force of two polymers increased simultaneously. Accordingly, molding blends with stable and durable hydrophobility were successfully gained based on migration of silicone and entanglement of alkane and PP. It’s noticeable that the water contact angle of the blend remained to be about 106° from 113°, even soaking in acid (pH = 1) and alkali (pH = 14) solutions, deionized water and anhydrous ethanol, or under multiple strong frictions. This will provide a facile and effective strategy to endow general materials with durable antifouling properties directly by injection molding without additional coating.

A Novel Catalytic System of [O,O] Bidentate Titanium Complexes and Et2AlCl/Bu2Mg for the Production of Ultra‐High Molecular Weight Polyethylene

AbstractA bidentate ligand, 2,3‐dihydro‐2,2‐dimethyl‐7‐benzofuranol (ddbfOH), is used to synthesize the titanium complexes, ddbfOTi(OiPr)3(1) and (ddbfO)2Ti(OiPr)2(2). Combined with diethylaluminium chloride (Et2AlCl) and di‐n‐butylmagnesium (Bu2Mg), complexes 1 and 2 exhibit super high activity towards ethylene polymerization, and giving the ultra‐high molecular weight polyethylene (UHMWPE). After rationally optimizing the experimental conditions, the highest polymerization activity is achieved in both 1/ and 2/Et2AlCl/Bu2Mg catalytic systems (213.6×106 g‐PE⋅mol‐Ti−1 h−1, 142.8×106 g‐PE⋅mol‐Ti−1 h−1). The highest molecular weight (Mv =1905×104) can be achieved under a low polymerization temperature (−30 °C) at the expense of activity (3000 g‐PE⋅mol‐Ti−1 h−1). Additionally, through the investigation of various polymerization conditions on the activity and molecular weight of the catalytic system, we have found that the ratio of the catalyst and cocatalyst has a more significant impact on both activity and molecular weight.

Novel photoresponsive dinuclear nickel catalysts for ethylene (co)polymerization

Novel photoresponsive dinuclear nickel catalysts for ethylene (co)polymerization

Highly Active Immobilized Catalyst for Ethylene Polymerization: Neutral Single Site Y(III) Complex Bearing Bulky Silylallyl Ligand.

Exploring the surface organometallic chemistry on silica of highly electrophilic yttrium complexes is a relatively uncommon endeavor, particularly when focusing on tris-alkyl complexes characterized by Y-C σ-alkyl bonds. A drawback with this class of complexes once grafted on silica, is the frequent occurrence of alkyl transfer by ring opening of siloxane groups, resulting in a mixture of species. Herein, we employed a more stable homoleptic yttrium allyl complex bearing bulky η3-1,3-bis(trimethylsilyl)allyl ligand to limit this transfer reaction. This strategy has been validated by comparing the reactivity between [Y{ η3-1,3-C3H3(SiMe3)2}3] and [Y(o-CH2PhNMe2)3] with SiO2-700, where the undesired alkyl transfer reaction occurred for [Y(o-CH2PhNMe2)3] leading to a bipodal [(≡SiO)2Y(o-CH2PhNMe2)] as major surface species, 2, while [Y{ η 3-1,3-C3H3(SiMe3)2}3] resulted selectively in a monopodal species, [(≡SiO)Y{η3-1,3-C3H3(SiMe3)2}2], 1. The materials obtained were characterized by DRIFT, solid state NMR, mass balance analysis and EXAFS. Catalyst 1 showed high activity compared to 2 in ethylene polymerization. The catalytic performance of this neutral catalyst 1 was extended to pre-industrial scale in the presence of hydrogen and 1-hexene. An unprecedented activity, up to 7400 gPE gcat -1 h-1 was obtained even with very low concentration of scavenger AliBu3 (TIBA/Y=1.2). The obtained HDPE exhibited desired spherical particle morphology with broad molar mass distribution.

Intelligent Reversible Reconfigurable Metamaterials Based on a Two-Way Shape Memory Polymer.

The development of intelligent reversible reconfigurable metamaterials has great significance in constructing three-dimensional metamaterials and introducing reversible tunability into metamaterials. Here, we introduce an intelligent metamaterial consisting of a two-way shape memory polymer (2W-SMP) ethylene vinyl acetate copolymer (EVA) actuator substrate and a patterned flexible-rigid film. Mechanical buckling of the 2W-SMP substrate was controlled by thermal stimulation. This makes it possible to afford an ability to initiate 3D structure formation or shape reconfiguration remotely in an on-demand fashion. In addition, the shape of the 2W-SMP substrate is temperature-dependent, allowing repeatable reversible deformation through temperature control after a single programming. Therefore, the electromagnetic properties of metamaterials can also be repeatedly and reversibly tuned between 9.15 and 10.82 GHz. Experimental demonstrations include the deformation and tunable electromagnetic properties of intelligent reversible reconfigurable metamaterial cells. The results create many opportunities for advanced programmable three-dimensional metamaterials.

Designing of imine thiophene-ligated metal-complexes and implication in ethylene polymerization

Polyethylene is the single largest volume polymer produced globally using Ziegler-type catalysts. Numerous modifications have been reported in search of a better catalyst that can control molecular weight, polydispersity, and branching. In our attempts to identify a suitable imine thiophene-ligated chromium complex, we examined 9 different titanium complexes computationally. The DFT investigations considered barriers for insertion, propagation, and termination by β-H elimination or chain transfer, and identified N-(4-methoxyphenyl)-2-phenyl-1-(thiophen-2-yl)ethan-1-imine(L9) as the most suitable ligand. Subsequently, L9 was prepared in good yield (70%) by condensing 2-phenyl-1-(thiophen-2-yl)ethan-1-one with 4-methoxyaniline. Ligand L9 was treated with early transition metal precursors (Ti, Cr, Zr) to generate a homogenous catalyst. The identity of these catalysts was unambiguously ascertained using a combination of NMR, ICP, FT-IR, UV-Vis spectroscopy, and ESI-MS. The performance of L9-ligated titanium complex [Cat.1] was examined in ethylene polymerization using MMAO as a co-catalyst. Insertion of ethylene was tracked using high-pressure NMR experiments and Cat.1 was found to be active in the polymerization. Ethylene polymerization conditions were optimized to obtain high activity and molecular weight polyethylene. The chromium complex [Cat.2] outperformed the Ti and Zr-derived catalysts with the highest TOF of 6294 mol of PE/mol of Cr/h. Cat.2 produced high molecular weight, high-density polyethylene.

Achieving Linear α-Macro-olefins in Ethylene Polymerization through Precisely Tuned Bis(imino)pyridylcobalt Precatalysts with Steric and Electronic Parameters

Achieving Linear α-Macro-olefins in Ethylene Polymerization through Precisely Tuned Bis(imino)pyridylcobalt Precatalysts with Steric and Electronic Parameters

Faster and greater moisture curing ethylene‐silane copolymers with good shelf stabilities

AbstractVinyltrimethoxysilane (VTMS) functionalized ethylenic polymers, in the form of reactor‐made ethylene‐silane copolymers as well as post‐reactor made silane‐grafted ethylene polymers, were evaluated for the purpose of moisture‐induced crosslinking through hydrolysis and condensation reactions. The copolymers were of 1.6 wt% or 4.2 wt% VTMS contents, and the silane‐grafted resins ranged in VTMS contents from 1.1 to 3.7 wt%. The silane‐grafted materials were very reactive under humid conditions at room temperature, resulting in very poor shelf stabilities manifested in sharp drops in their melt indices over time (changes that in the early stages were dominated mostly by resin molecular weight distribution and/or branching, and in the later stages much more by silane content). In sharp contrast, the ethylene‐silane copolymers exhibited outstanding shelf stabilities over time even at relatively high silane content, indicating desirably low reactivities in the absence of moisture‐cure catalyst. When formulated with catalyst, and exposed to humid conditions, the cure characteristics of the silane functionalized ethylene polymers varied significantly, with the fastest and greatest crosslinking observed using the ethylene‐silane copolymer of 4.2 wt% VTMS content and remarkably excellent shelf stability. Analyses of reaction rates revealed very interesting trends, depending on type of catalyst (tin or sulfonic acid) and resin.Highlights Ethylene‐silane copolymers and silane‐grafted ethylene polymers were studied. Copolymers exhibited vastly superior shelf stabilities than grafted materials. Catalyst type and loading affected moisture‐induced crosslinkability. Increased silane content in copolymer led to faster and greater crosslinking. Best balance of crosslinkability and shelf stability obtained with copolymers.

P-Aryl-Substituted Iminopyridine Chromium Complexes as Precatalysts for Ethylene Polymerization: The Question of the Physical Oxidation State Examined by Experimental and Density Functional Study in the Absence of Structural Data

<i>p</i>-Aryl-Substituted Iminopyridine Chromium Complexes as Precatalysts for Ethylene Polymerization: The Question of the Physical Oxidation State Examined by Experimental and Density Functional Study in the Absence of Structural Data

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.

Synthesis of Ultralow-Density Polyethylene Elastomers Using Triarylnaphthyl Iminopyridyl Ni(II) Catalysts.

Recently, the chain-walking ethylene polymerization strategy has garnered widespread attention as an efficient and straightforward method for preparing polyolefin elastomers. In this study, a series of 2,4,8-triarylnaphthyl iminopyridyl nickel catalysts were synthesized and used in ethylene polymerization. These catalysts demonstrated moderate catalytic activity (105 g mol-1 h-1), producing high-molecular-weight (up to 145.5 kg/mol) polyethylene materials with high branching degrees (75-95/1000C) and correspondingly low melting points. Detailed analysis using 13C NMR spectroscopy revealed that the polyethylenes primarily featured methyl and long-chain branches. Mechanical testing of the polyethylene samples obtained from catalysts Ni1-Ni3 exhibited moderate stress at break (4.64-6.97 MPa) coupled with a very high strain at break (1650-3752%), indicating their very good ductility. Furthermore, these polyethylenes showcased great elastic recovery abilities, with strain recovery values ranging from 72% to 85%. In contrast, the polyethylene produced by Ni4 displayed notably inferior tensile strength (0.16 MPa) and tensile recovery (43%). To the best of our knowledge, this study represents the inaugural utilization of a nickel iminopyridyl catalyst in the preparation of a polyethylene thermoplastic elastomer.

Synthesis of linear low-density polyethylene waxes through chain-walking benzocycloalkyl nickel-catalyzed ethylene polymerization

Polyethylene wax is a highly useful material, and its diverse topological structures may have a significant impact on its applications. In this study, we have devised and synthesized a series of unilateral benzocycloalkyl α-diimine nickel catalysts. These nickel catalysts exhibited very high activities (1.06 to 10.25 × 106 g mol-1·h-1) and yielded branched (37–97/1000 C) polyethylene waxes with low molecular weights (Mn = 0.49 to 2.01 kg mol-1) and variable molecular weight distributions (1.79–35.05) in ethylene polymerization. Polymerization conditions such as pressure and temperature and catalyst structure such as backbone and axial substituents have an important influence on the polymerization activity and the properties of the resulting polyethylene waxes. High-temperature NMR reveals that these branched polyethylenes primarily feature short-chain branches, such as the methyl group, and exhibit a topology resembling that of low-molecular-weight linear low-density polyethylene (LLDPE).

Nickel-catalyzed in situ synthesis of UHMWPE/TiO2 composites with enhanced mechanical properties and adjustable photocatalytic degradabilities

Expanding the application field of polyolefin materials through functionalization has been a research hotspot in the past three decades. Here, a TiO2-supported anilinenaphthoquinone nickel catalyst was assembled and applied for in situ ethylene polymerization with high activity (>2000 kg mol–1h−1) to produce ultra-high molecular weight polyethylene (UHMWPE)/TiO2 composites with unique physicochemical performance. The UHMWPE/TiO2 composite films and fibers prepared by in-situ ethylene polymerization are superior to the samples from the blend system in issues such as TiO2 dispersibility, mechanical property, and photocatalytic degradability. The mechanical properties (strength up to 26.8 cN/dtex, modulus up to 1248.8 cN/dtex) of the obtained UHMWPE/TiO2 composite fibers are significantly improved with a very low dosage of TiO2 (as low as 1.4 wt‰). Moreover, UHMWPE/TiO2 composites obtained by coating Al2O3 and SiO2 on the surface of TiO2 not only retain the strong absorption of ultraviolet rays, but also effectively weaken the photocatalytic degradation effect.

Simulation and study of the flow field in a kettle-type reactor for ethylene polymerization

Abstract Addressing the complexities inherent in the polymerization process for solution method polyethylene production, particularly the challenges in describing the turbulent three-dimensional flow field within the reactor and the precise design of reactor structural parameters, this research leverages computational fluid dynamics (CFD) methods integrated with polymerization reaction kinetics equations. We have formulated User-Defined Functions (UDFs) for a quantitative representation of the polymerization process. Employing the Realizable k-epsilon turbulence model and Sliding Grid (SG) technique, we analyzed the flow dynamics and field distribution within the reactor, elucidating the distribution patterns of temperature, pressure, and concentration fields. A comparative assessment of simulation outcomes against experimental data revealed that the average deviation of the simulated temperature field from actual operating conditions falls within the permissible error range, thereby affirming the simulation model’s validity. Utilizing local sensitivity analysis, we investigated the impact of impeller structural parameters on mixing time and stirring power. Our analysis of the most sensitive structural parameters indicated that impeller diameter and the number of impellers are pivotal in reducing mixing time and stirring power, respectively. Notably, the stirring power escalates with an increase in the number of impellers, while the mixing time exhibits a trend of initial decrease followed by an increase with varying impeller diameters. The methodologies and patterns discerned in this study provide insightful design references for the design and optimization of reactors across different tonnages.

Binary Mixtures (AlknAlCl3–n + Alk2Mg) as Catalyst Components for Ethylene Polymerization and the Role of Titanium Oxidation State in Their Catalytic Activity

Binary Mixtures (AlknAlCl3–n + Alk2Mg) as Catalyst Components for Ethylene Polymerization and the Role of Titanium Oxidation State in Their Catalytic Activity