Recent advancements in α-diimine-nickel and -palladium catalysts for ethylene polymerization

Study of Heterogeneity of Ethylene/1-Octene Copolymers Synthesized with Zirconium and Titanium Complexes Bearing Diamine-bis(phenolate) Ligands

A series of ethylene/1-octene copolymers synthesized with diamine-bis(phenolate) complexes activated with Al(iBu)3/[Ph3C][B(C6F5)4] were subjected to preparative temperature rising elution fractionation (TREF). The complexes used differed in the type of metallic center (Zr or Ti) or the amine donor in the pendant arm of the ligand (NMe2 or NiPr2). The obtained fractions were then characterized via FTIR, DSC and GPC methods. It was found that all the copolymers had very broad chemical composition distributions, and the most heterogeneous was the copolymer produced by the titanium complex bearing a ligand with the NiPr2 donor group. The difference in the comonomer incorporation into the macromolecules of the fractions was as high as 8.3 mol%. The melting temperature and molecular weight of the fractions changed nearly linearly with the increased elution temperature. Copolymers produced by zirconium catalysts were also fractionated by molecular weight using the solvent/non-solvent technique with subsequent analysis of the fractions. It was shown that the fractions have a similar composition, low molecular weight distribution and very broad comonomer distribution. Therefore, the comonomer content in the fractions was not a function of the molecular weight as was observed for the copolymers synthesized with the Ziegler-Natta catalysts.

Enhancing isoprene polymerization with high activity and adjustable monomer enchainment using cyclooctyl-fused iminopyridine iron precatalysts

In this study, a series of structurally rigid cyclooctyl-fused iminopyridine iron complexes, [L2FeCl][FeCl4] and [2L3Fe][Cl][3FeCl4], was synthesized via a one-pot method and investigated as precatalysts in conjunction with methylaluminoxane for isoprene (Ip) polymerization. Combined characterization through FTIR analysis, elemental analysis and single crystal XRD analysis fully verified the structure of these complexes. The most active iron complex, FeH, exhibited a trisligated nature, with its cation adopting an octahedral geometry around the metal center. In contrast, all the other iron complexes (Fe2Me, Fe2Et, Fe2iPr, Fe3Me, Fe2Et,Me) displayed bisligated configurations, with distorted trigonal bipyramidal geometry of cations. During isoprene polymerization, the extent of steric hindrance of the ligand framework exerted a significant impact on catalytic performance. The FeH precatalyst with less steric hindrance demonstrated excellent performance, producing high molecular weight polyisoprenes with conversions exceeding 99% for 4000 equiv. of monomer. Even at very low catalyst loadings, as low as 0.0025 mol% (Fe/Ip), the polymerization of isoprene could proceed smoothly with an exceptionally high activity of 4.0 × 106 gPI (molFe, h)-1. Moreover, this precatalyst exhibited good thermal stability, maintaining high activity levels (typically 105 gPI (molFe, h)-1) across a broad temperature range from -20 °C to 100 °C. Additionally, by adjusting steric substituents and the reaction temperature, the 1,4/3,4 regioselectivity could be modulated from 9/91 to 69/31 while maintaining a high stereoselectivity of cis-1,4 structures (cis/trans: >99/1).

Design, fabrication, evaluation, and in vitro study of green biomaterial and antibacterial polymeric biofilms of polyvinyl alcohol/tannic acid/CuO/ SiO2

In this study, a three-component biofilm for rapid wound dressing consisting of polyvinyl alcohol (PVA)/tannic acid (TA)/with CuO/SiO2 with different percentages (0, 5, 10, and 15 wt% NPs) is evaluated. In addition to controlling bleeding and absorption of blood and wound secretions, it protects the damaged tissue from the attack of microbes. It protects against viruses and thus reduces the treatment time. Analysis of biofilms morphology is performed by Field emission scanning electron microscopy (FE-SEM), phases in biofilms were analyzed by X-ray diffraction (XRD) analysis, chemical bonds, and functional groups are analyzed by Fourier transform infrared (FTIR) spectroscopy, and mechanical tests are performed to evaluate the strength of the samples. The thermogravimetric analysis (TGA) is applied to estimate the thermal stability of the biopolymer films with various percentages of CuO/SiO2 nanoparticles. Also, antibacterial test, bioactivity of the biofilms, the percentage of swelling ratio, and porosity of the samples were examined by immersing the samples in simulated body fluid (SBF) and Phosphate-buffered saline (PBS) for 14 days in vitro. The composite makeup of the TA/PVA sample, comprising 15 wt % CuO/SiO2 and containing 15 wt% of nanoparticles, exhibited superior heat resistance compared to other samples by an increase of 50 °C. This improvement can be attributed to the nanoparticles reaching their saturation point. The swelling ratio was assessed in both SBF and PBS, and in both instances, the sample increased by up to 10 wt% before decreasing, indicating the saturation of the nanoparticles.

Microstructural Characteristics of High-Pressure Die Casting with High Strength-Ductility Synergy Properties: A Review

In response to the increased emphasis on reducing carbon emissions, the demand for lightweight, high-performance structural materials is quickly increasing, and Mg alloys, because of their having the lowest density among the common engineering metals, have demonstrated considerable advantages and prospective applications in contemporary industry. High-pressure die casting (HPDC), owning to its high efficiency and low production cost, is the most extensively utilized technique in commercial Mg alloy applications. The high room-temperature strength-ductility of HPDC Mg alloys plays an important role in their safe use, particularly in the automotive and aerospace industries. With respect to HPDC Mg alloys, their mechanical properties highly rely on their microstructural characteristics, particularly the intermetallic phases, which are further dependent on the alloys' chemical compositions. Therefore, the further alloying of traditional HPDC Mg alloys, such as Mg-Al, Mg-RE, and Mg-Zn-Al systems, is the most adopted method to further improve their mechanical properties. Different alloying elements lead to different intermetallic phases, morphologies, and crystal structures, which can have helpful or harmful effects on an alloy's strength or ductility. The methods aimed at regulating and controlling the strength-ductility synergy of HPDC Mg alloys have to arise from an in-depth understanding of the relationship between the strength-ductility and the components of the intermetallic phases of various HPDC Mg alloys. This paper focuses on the microstructural characteristics, mainly the intermetallic phases (i.e., components and morphologies), of various HPDC Mg alloys with good strength-ductility synergy, aimed at providing insight into the design of high-performance HPDC Mg alloys.

CeO2-Supported TiO2-Pt Nanorod Composites as Efficient Catalysts for CO Oxidation

Supported Pt-based catalysts have been identified as highly selective catalysts for CO oxidation, but their potential for applications has been hampered by the high cost and scarcity of Pt metals as well as aggregation problems at relatively high temperatures. In this work, nanorod structured (TiO₂-Pt)/CeO₂ catalysts with the addition of 0.3 at% Pt and different atomic ratios of Ti were prepared through a combined dealloying and calcination method. XRD, XPS, SEM, TEM, and STEM measurements were used to confirm the phase composition, surface morphology, and structure of synthesized samples. After calcination treatment, Pt nanoparticles were semi-inlayed on the surface of the CeO₂ nanorod, and TiO₂ was highly dispersed into the catalyst system, resulting in the formation of (TiO₂-Pt)/CeO₂ with high specific surface area and large pore volume. The unique structure can provide more reaction path and active sites for catalytic CO oxidation, thus contributing to the generation of catalysts with high catalytic activity. The outstanding catalytic performance is ascribed to the stable structure and proper TiO₂ doping as well as the combined effect of Pt, TiO₂, and CeO₂. The research results are of importance for further development of high catalytic performance nanoporous catalytic materials.

Transition Metal-(μ-Cl)-Aluminum Bonding in α-Olefin and Diene Chemistry

Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M−(μ-Cl)−Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially more important industrial processes such as oligomerization and polymerization of α-olefins and conjugated dienes. Numerous publications indirectly point at the significance of M−(μ-Cl)−Al bonding in Ziegler−Natta and related transformations, but only a few studies contain experimental or at least theoretical evidence of the involvement of M−(μ-Cl)−Al species into catalytic cycles. In the present review, we have compiled data on the formation of M−(μ-Cl)−Al complexes (M = Ti, Zr, V, Cr, Ni), their molecular structure, and reactivity towards olefins and dienes. The possible role of similar complexes in the functionalization, oligomerization and polymerization of α-olefins and dienes is discussed in the present review through the prism of the further development of Ziegler−Natta processes and beyond.

Comparative Evaluation of Various Extraction Techniques for Secondary Metabolites from Bombax ceiba L. Flowering Plants along with In Vitro Anti-Diabetic Performance

Bombax ceiba L. (Family: Malvaceae) was rightly called the “silent doctor” in the past as every part of it had medicinal value. For centuries, humans have used this plant according to the traditional medicinal systems of China, Ayurveda, and tribal communities. Recently, with an emerging interest in herbals, attention has been paid to scientifically validating medicinal claims for the treatment of diabetes using secondary metabolites of B. ceiba L. flowers. In the present study, specific secondary metabolites from the flowers of B. ceiba L. were isolated in good yield using the solvent extraction methodology, and their in vitro anti-diabetic efficacy was examined. Extraction efficiency of each solvent for secondary metabolites was found in following order: water > ethanol> methanol > chloroform > petroleum ether. Quantitative analysis of secondary metabolites showed 120.33 ± 2.33 mg/gm polyphenols, 60.77 ± 1.02 mg/g flavonoids, 60.26 ± 1.20 mg/g glycosaponins, 0.167 ± 0.02 mg/g polysaccharides for water extract; 91.00 ± 1.00 mg/g polyphenols, 9.22 ± 1.02 mg/g flavonoids, 43.90 ± 0.30 mg/g glycosaponins, 0.090 ± 0.03 mg/g poly saccharides for ethanol extract; 52.00 ± 2.64 mg/g polyphenols, 35.22 ± 0.38 mg/g flavonoids, 72.26 ± 1.05 mg/g glycosaponins, 0.147 ± 0.01 mg/g polysaccharides for methanol extract; 11.33 ± 0.58 mg/g polyphenols, 23.66 ± 1.76 mg/g flavonoids, 32.8 ± 0.75 mg/g glycosaponins, 0.013 ± 0.02 mg/g polysaccharides for chloroform extract; and 3.33 ± 1.53 mg/g polyphenols, 1.89 ± 1.39 mg/g flavonoids, 21.67 ± 1.24 mg/g glycosaponins, 0.005 ± 0.01 mg/g polysaccharides for petroleum ether extract. Glucose uptake by yeast cells increased 70.38 ± 2.17% by water extract.

Recent Advances in the Copolymerization of Ethylene with Polar Comonomers by Nickel Catalysts

The less-expensive and earth-abundant nickel catalyst is highly promising in the copolymerization of ethylene with polar monomers and has thus attracted increasing attention in both industry and academia. Herein, we have summarized the recent advancements made in the state-of-the-art nickel catalysts with different types of ligands for ethylene copolymerization and how these modifications influence the catalyst performance, as well as new polymerization modulation strategies. With regard to α-diimine, salicylaldimine/ketoiminato, phosphino-phenolate, phosphine-sulfonate, bisphospnine monoxide, N-heterocyclic carbene and other unclassified chelates, the properties of each catalyst and fine modulation of key copolymerization parameters (activity, molecular weight, comonomer incorporation rate, etc.) are revealed in detail. Despite significant achievements, many opportunities and possibilities are yet to be fully addressed, and a brief outlook on the future development and long-standing challenges is provided.

Structural evolution of iminopyridine support for nickel/palladium catalysts in ethylene (oligo)polymerization

The interest in the late transition metal catalyst based design of new architectures of polyethylene (PE) has continuously been increasing over the last few years. The structure of these catalysts is predominantly important in controlling the morphological and architectural properties of the resulting polyethylene. Particularly, iminopyridine is a versatile bidentate support for Ni and Pd catalysts in ethylene (oligo)polymerization providing a wide variety of products ranging from volatile oligomers to ultra-high molecular weight polyethylene. Extensive structural modifications have been induced in the iminopyridine ligand through steric and electronic substitution, tuning the catalyst behavior in terms of activity and properties of the resulting polymer. Carbocyclic-fused iminopyridine and N-oxide iminopyridine are the new state of the art iminopyridine ligand designs. In this review, we aim to summarize all the developments in mononuclear iminopyridine-nickel and -palladium catalysts for ethylene (oligo)polymerization since the first report published in 1999 to present, focusing on the correlation among the pre-catalyst, co-catalyst type, thermal stability and polymer/oligomer structure. For comparison, the structural variations in the binuclear iminopyridine-nickel catalysts are also described. The detailed comparison of the structural variations in these catalysts with respect to their polymerization performance will give deep understanding in the development of new efficient catalyst designs.

Late Transition Metal Catalysts with Chelating Amines for Olefin Polymerization

Polyolefins are the most consumed polymeric materials extensively used in our daily life and are usually generated by coordination polymerization in the polyolefin industry. Olefin polymerization catalysts containing transition metal–organic compound combinations are undoubtedly crucial for the development of the polyolefin industry. The nitrogen donor atom has attracted considerable interest and is widely used in combination with the transition metal for the fine-tuning of the chemical environment around the metal center. In addition to widely reported olefin polymerization catalysts with imine and amide donors (sp2 hybrid N), late transition metal catalysts with chelating amine donors (sp3 hybrid N) for olefin polymerization have never been reviewed. In this review paper, we focus on late transition metal (Ni, Pd, Fe, and Co) catalysts with chelating amines for olefin polymerization. A variety of late transition metal catalysts bearing different neutral amine donors are surveyed for olefin polymerization, including amine–imine, amine–pyridine, α-diamine, and [N, N, N] tridentate ligands with amine donors. The relationship between catalyst structure and catalytic performance is also encompassed. This review aims to promote the design of late transition metal catalysts with unique chelating amine donors for the development of high-performance polyolefin materials.