Uniform shape monodisperse single chain nanocrystals by living aqueous catalytic polymerization

A Versatile Route to Shape Polymer Nanoparticles by Deforming Nanoreactors Made from Magnetic Surfactants

Directions are equivalent in an amorphous system, so anisotropy cannot emerge of its own accord, resulting in a gap for preparing polymer nanoparticles deviating from a spherical shape. Unlike inorganic nanocrystals for which faceting controls shape, polymers are not directly available as rod-like particles, for instance. Here, we show a highly versatile, nontoxic, novel approach to break this paradigm and obtain polymer nanorods by emulsion polymerization using a unique surfactant comprising a magnetic head group. Surprisingly, even applying a weak magnetic field to the magnetic surfactant within an emulsion polymerization transforms diamagnetic polymers into rod-like nanoparticles instead of their usual spherical shapes. The polarization in a magnetic field exerts a torque on the molecular structure, and as a result, the emulsion droplets deform. The method can be applied to different polymers such as polystyrene, polymethylmethacrylate, or polythiophene. The magnetic surfactant is recovered quantitatively and can be reused; one obtains metal-free polymer particles, and the process is sustainable. The straightforward approach presented here will unlock several applications of these previously inaccessible polymer nanorods, particularly in the case of conducting polymers.

Aqueous Catalytic Olefin Polymerization With Nickel and Palladium Catalysts

Polyolefins are extensively used in modern society, with hydrocarbon organic compounds traditionally serving as solvents for their preparation. Water, as a reaction medium, offers significant advantages, including non-flammability, non-toxicity, high specific heat capacity, and strong polarity. A promising avenue of research involves replacing organic media with water in polymerization reactions, which could yield considerable economic benefits. Among the various transition metal catalysts used to synthesize polyolefins, late-transition metal catalysts, such as Ni(II) and Pd(II) catalysts, demonstrate enhanced tolerance to polar groups, making them particularly suitable for aqueous polymerization of olefins. This review focuses on the Ni(II) and Pd(II) catalysts utilized for the aqueous catalytic polymerization of olefins, as well as various types of polyolefins fabricated. Key aspects encompass designs of catalysts, polymerization systems, monomers, and material microstructures. The preparation of ultra-high molecular weight polyethylene (UHMWPE) nanocrystals and the modulation of polymer morphology are highlighted. The possible development trend of aqueous catalytic polymerization is envisioned to achieve the development concept of environmental protection and the needs of industrial production.

Controlled oligomerization in water to hyperbranched ethylene oligomers

The production of high molecular weight polyethylene particles in aqueous environments has received considerable attention, yet reports on the formation of polyethylene oil within water remain scarce. Herein, we present findings that demonstrate the oligomerization of ethylene by certain iminopyridyl Pd(II) catalysts in water, resulting in the synthesis of hyperbranched ethylene oligomers. It is worth highlighting the intriguing observation that these catalysts exhibited a remarkable catalytic longevity in aqueous medium and ultimately facilitated the generation of a substantial liquid polyolefin phase from water. 13C NMR and viscosity measurements indicate that the resultant polyethylene oils are characterized by prevalent long-chain branching and a very low viscosity.

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.

Aqueous Keto-Polyethylene Dispersions from Catalytic Copolymerization of Ethylene and Carbon Monoxide in Water

Water-soluble [P,O]Ni(II) catalysts enable the direct catalytic nonalternating copolymerization of fundamental comonomers ethylene and carbon monoxide (CO) in water as an environmentally friendly reaction medium. This yields stable aqueous dispersions of high molecular weight polyethylene containing ∼1 mol % of largely isolated in-chain keto groups in the form of particles with sizes between 100 nm and 1 μm. The intermediate species of chain growth resulting from incorporation of polar comonomers are amenable to specific chain termination pathways in conjunction with water.

Recent Advancements in the Synthesis of Ultra-High Molecular Weight Polyethylene via Late Transition Metal Catalysts

Ultra-high molecular weight polyethylenes (UHMWPEs) are significant engineering plastics for their unique properties, such as high impact resistance, abrasion resistance, weatherability, lubricity, and chemical resistance. Consequently, developing a suitable catalyst is vital in facilitating the preparation of UHMWPE. The late transition metal catalysts have emerged as effective catalysts in producing UHMWPE due to their availability, enhanced tolerance to heteroatom groups, active polymerization characteristics, and good copolymerization ability with polar monomers. In this review, we mainly focus on the late transition metal catalysts, summarizing advancements in their application over the past decade. Four key metals (Ni, Pd, Fe, Co) for generating linear or branched UHMWPE will be primarily explored in this manuscript.

Aqueous Coordination-Insertion Copolymerization for Producing High Molecular Weight Polar Polyolefins

Hydrocarbons, when used as the medium for transition metal catalyzed organic reactions and olefin (co-)polymerization, are ubiquitous. Environmentally friendly water is highly attractive and long-sought, but is greatly challenging as coordination-insertion copolymerization reaction medium of olefin and polar monomers. Unfavorable interactions from both water and polar monomer usually lead to either catalyst deactivation or the formation of low-molecular-weight polymers. Herein, we develop well-behaved neutral phosphinophenolato nickel catalysts, which enable aqueous copolymerization of ethylene and diverse polar monomers to produce significantly high-molecular-weight linear polar polyolefins (219-549 kDa, 0.13-1.29 mol %) in a single-component fashion under mild conditions for the first time. These copolymerization reactions occur better in water than in hydrocarbons such as toluene. The dual characteristics of high molecular weight and the incorporation of a small amount of functional group result in improved surface properties while retain the desirable intrinsic properties of high-density polyethylene (HDPE).

A Sustainable Method for Removal of the Full Range of Liquid and Solid Hydrocarbons from Water Including Up- and Recycling

Beyond their CO2 emittance when burned as fuels, hydrocarbons (HCs) serve as omnipresent raw materials and commodities. No matter if as liquid oil spills or the endless amounts of plastic roaming the oceans, HCs behave as persistent pollutants with water as main carrier to distribute. Even if their general chemical structure [-(CH2 )n -] is quite simple, the endless range of n leads to contaminations of different appearances and properties. A water remediation method based on superparamagnetic iron oxide nanoparticles (SPIONs) modified with self-assembled monolayers of alkyl phosphonic acid derivatives is presented. These molecules enable the SPIONs to non-covalently bind HCs, independently from the molecular weight, size and morphology. The attractive interaction is mainly based on hydrophobic and Coulomb interaction, which allows recycling of the SPIONs. The superparamagnetic core allows a simple magnetic collection and separation from the water phase which makes it a promising addition to wastewater treatment. Agglomerates of collected plastic "waste" even exhibit superior adsorption properties for crude oil, another hydrocarbon waste which gives these collected wastes a second life. This upcycling approach combined with presented recycling methods enables a complete recycling loop.

Multimorphological Remoldable Silver Nanomaterials from Multimode and Multianalyte Colorimetric Sensing to Molecular Information Technology

Inspired by life's interaction networks, ongoing efforts are to increase complexity and responsiveness of multicomponent interactions in the system for sensing, programmable control, or information processing. Although exquisite preparation of single uniform-morphology nanomaterials has been extremely explored, the potential value of facile and one-pot preparation of multimorphology nanomaterials has been seriously ignored. Here, multimorphological silver nanomaterials (M-AgN) prepared by one pot can form interaction networks with various analytes, which can be successfully realized from multimode and multianalyte colorimetric sensing to molecular information technology (logic computing and security). The interaction of M-AgN with multianalytes not only induces multisignal responses (including color, absorbance, and wavelength shift) for sensing metal ions (Cr3+, Hg2+, and Ni2+) but also can controllably reshape its four morphologies (nanodots, nanoparticles, nanorods, and nanotriangles). By abstracting binary relationships between analytes and response signals, multicoding parallel logic operations (including simple logic gates and cascaded circuits) can be performed. In addition, taking advantage of natural concealment and molecular response characteristics of M-AgN nanosystems can also realize molecular information encoding, encryption, and hiding. This research not only promotes the construction and application of multinano interaction systems based on multimorphology and multicomponent nanoset but also provides a new imagination for the integration of sensing, logic, and informatization.

Phase Transformation in UHMWPE Reactor Powders Synthesized on Various Catalysts in Mechanical and Thermal Fields

Nowadays, a solvent-free method for production of high performance fibers directly from ultrahigh-molecular-weight polyethylene (UHMWPE) reactor powder is being actively developed. It causes the interest in the morphology of the reactor particles and their behavior in thermal and mechanical fields. Changes in the phase composition in virgin particles of ultra-high molecular-weight polyethylene reactor powders and in particles of powders compressed at room temperature under different pressures were studied in real time using synchrotron radiation with heating in the range of 300-370 K. It was found that the content of the monoclinic phase in reactor powders depends on the type of catalyst used for synthesis and on the applied pressure. It is shown that there are monoclinic phases of different nature: a structurally stabilized monoclinic phase formed during synthesis, and a monoclinic phase resulting from plastic deformation during compaction at room temperature. The behavior of these phases in temperature and mechanical fields is compared.

Access to Disentangled Ultrahigh Molecular Weight Polyethylene via a Binuclear Synergic Effect

Disentangled ultrahigh molecular weight polyethylene (dis-UHMWPE) has excellent processability but can be achieved under extreme conditions. Herein, we report ethylene polymerization with the binuclear half-sandwich scandium complexes C1-Sc₂ and C2-Sc₂ to afford UHMWPE. C1-Sc₂ bearing a short linker shows higher activity and gives higher molecular weight PEs than C2-Sc₂ containing a flexible spacer and the mononuclear Sc₁ . Strikingly, all UHMWPEs isolated from C1-Sc₂ under broad temperature range (25-120 °C) and wide ethylene pressures (2-13 bar) feature very low degree of entanglement as proved by rheological test, DSC annealing study and SEM. These dis-UHMWPEs are facilely mediated solid-state-process at 130 °C and their tensile strength and modulus reach up to 149.2 MPa and 1.5 GPa, respectively. DFT simulations reveal that the formation of dis-UHMWPE is attributed to the binuclear synergic effect and the agostic interaction between the active center and the growing chain.

Hydrophilic Catalysts with High Activity and Stability in the Aqueous Polymerization of Ethylene to High-Molecular-Weight-Polyethylene

Water-soluble synthetic transition metal catalysts have been studied extensively for many reactions, but for olefin polymerization such catalysts have been lacking. We report herein a straightforward synthesis of phosphinephenolato NiII catalysts endowed permanently with a hydrophilic sulfonate moiety bound to the chelating ligand. These catalysts' hydrophilic active sites promote aqueous ethylene polymerization with high activity (TOF up to 6.3×104  molEthylene  molNi -1  h-1 ) to high molecular weight polyethylene (HDPE), with half-lives on the order of hours also at elevated temperatures. The obtained polyethylene dispersions feature narrow particle size distributions without any aggregates.

Precursor Heterogeneity Driven Mo-Te Nanoparticle Structural Diversification for Cancer Photo-Theranostics

Chemical reactions between homogeneous precursors are typically used to synthesize monodisperse nanoparticles with well-controlled size and morphology. It is difficult to predict the evolved nanostructures when using two heterogeneous precursors. In this study, three types of Mo-Te nanoparticles shaped like leaves, spindles, and rice grains (denoted respectively as nanoleaf, nanospindle, and nanorice) were obtained from dextrose-mediated proton-coupled electron transfer reaction between the solid polyoxomolybdate (POM) and the ionic tellurite anion as precursors. All produced nanoparticles had excellent optical absorption in the ultraviolet(UV)-visible(Vis)-near-infrared(NIR) regions, with only slight deviations among them. After confirming nanoparticles' photothermal conversion and photocatalytic activity at multiple wavelengths, the Mo-Te nanorice was tested as a potential agent for cancer treatment due to its minimum toxicity, excellent colloidal stability, and intrinsic anticancer effect. Excellent treatment efficacy and clearance were confirmed in vitro and in vivo. Due to their photoacoustic imaging capability, the injection of pristine nanoparticles could also realize phototheranostics without using additional drugs, probes, or photosensitizers.

Living Aqueous Microemulsion Polymerization of Ethylene with Robust Ni(II) Phosphinophenolato Catalysts

Due to chain transfer events being competitive with chain growth, ethylene polymerization by P,O-chelated Ni(II) complexes usually affords low molecular weight polymers or oligomers. We now show that appropriately bulky substituted phosphinophenolato Ni(II) can polymerize in a living fashion, virtually devoid of chain transfer. Aqueous polymerizations with microemulsions of [κ²-P,O-2-(2-(2',6'-(MeO)₂C₆H₃)C₆H₄)(Ph)P-6-(3',5'-(CF₃)₂C₆H₃)C₆H₃O-NiMe(pyridine)] (3) at 30 °C yield polyethylenes with narrow molecular weight distributions (M_w/M_n 1.02 to 1.34) and ultrahigh molecular weights (up to 2 × 10⁶) in the form of aqueous nanoparticle dispersions. Catalyst stability and activity are maintained up to 70 °C in water.

Five shades of green: substituent influence on the (spectro-) electrochemical properties of diferrocenyl(phenyl)methylium dyes

Five new, intensely green diferrocenylphenylmethylium complexes 1+-5+ with electron donating (EDG: 4-MeO, 4-Me, 4-Br) or withdrawing (EWG: 3,5-CF₃, 4-ⁿC₆F₁₃) substituents were synthesized and fully characterized. The substituent influence on their electrochemical and spectroscopic properties was investigated by cyclic voltammetry, UV/Vis/NIR and T-dependent EPR spectroscopy of the cationic as well as the oxidized (12+-52+) and reduced (1˙-5˙) species. The reduced forms equilibrate with their corresponding dimers (65-83%) with a clear substituent influence as expressed by their Hammett parameters in an ordering 4+ > 5+ > 3+ > 2+ > 1+. The structures of all five precursor carbinols 1-OH-5-OH and those of three of the diferrocenylphenylmethylium cations (1+, 4+-5+) were established by X-ray crystallography.

Polyethylene materials with in-chain ketones from nonalternating catalytic copolymerization

[Figure: see text].

Terpyridine-Induced Folding of Anisotropic Polyphosphoester Platelets

The folding of macromolecules is of great importance in nature. Also in synthetic polymer chemistry, single-chain nanoparticles, i.e. folding synthetic macromolecules, are a current research topic to mimic protein folding and to generate well-defined structures. Here, we present the "folding" of anisotropic polymer platelets to further mimic natural folding processes on the (sub)micrometer scale. We report on the synthesis of terpyridine-functionalized long-chain polyphosphoesters by acyclic diene metathesis polymerization that can crystallize in dilute solution into anisotropic polymer crystal platelets. As the terpyridine units are expelled to the platelet surface, terpyridine-metal interactions could be induced by adding nickel(II) bis(acetylacetonate) (Ni(acac)₂) to the platelet dispersion in ethyl acetate. These polymer crystals were "folded" to homogeneous nanoparticles with a wrinkled structure, which were visualized by transmission electron microscopy (TEM). The size and size distribution of the obtained assemblies could be altered by varying the concentration of Ni(acac)₂. In contrast, no wrinkled structures but rather intrachain cross-linking was observed, when Ni(acac)₂ was added to the homogeneous polymer solution before crystallization. We believe that this concept of "folding" anisotropic polymer platelets will further enhance the control of morphologies on (sub)micrometer particles and might be useful for catalysis or separation.

Neutral Unsymmetrical Coordinated Cyclophane Polymerization Catalysts

Cyclophane structures can control steric pressure in the otherwise open spaces of square‐planar d⁸‐metal catalysts. This elegant concept was so far limited to symmetrical coordinated metals. We report how a cyclophane motif can be generated in ligands that chelate via two different donors. An ancillary second imine in the versatile κ²‐N,O‐salicylaldiminato catalyst type enables ring closure via olefin metathesis and selective double bond hydrogenation to yield a 30‐membered ring efficiently. Experimental and theoretical analyses show the ancillary imine is directed away from the active site and inert for catalysis. In ethylene polymerization the cyclophane catalyst is more active and temperature stable vs. an open structure reference, notably also in polar solvents. Increased molecular weights and decreased degrees of branching can be traced to an increased energy of sterically demanding transition states by the encircling cyclophane while chain propagation remains highly efficient.

Fluorinated α-Diimine Nickel Mediated Ethylene (Co)Polymerization

Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (F_n ; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given. As a notable result, the ortho-F substituted α-diimine nickel catalyst produced highly linear polyethylenes with an extremely high molecular weight (M_w =8703 kDa) and a significantly low degree of branching of 1.4/1000 C; however, the meta-F and/or para-F substituted α-diimine nickel catalysts generated highly branched (up to 80.2/1000 C) polyethylenes with significantly low molecular weights (M_w =20-50 kDa).

Coarse grained simulation of the aggregation and structure control of polyethylene nanocrystals

Polyethylene (PE) telechelics with carboxylate functional groups at both ends have been shown to assemble into hexagonal nanocrystal platelets with a height defined by their chain length in basic CsOH-solution. In this coarse grained (CG) simulation study we show how properties of the functional groups alter the aggregation and crystallization behavior of those telechelics. Systematic variation of the parameters of the CG model showed that important factors which control nanoparticle stability and structure are the PE chain length and the hydrophilicity and the steric demand of the head groups. To characterize the aggregation process we analyzed the number and size of the obtained aggregates as well as intramolecular order and intermolecular alignment of the polymer chains. By comparison of CG and atomistic simulation data, it could be shown that atomistic simulations representing different chemical systems can be emulated with specific, different CG parameter sets. Thus, the results from the (generic) CG simulation models can be used to explain the effect of different head groups and different counterions on the aggregation of PE telechelics and the order of the obtained nanocrystals.

Efficient Suppression of Chain Transfer and Branching via Cs -Type Shielding in a Neutral Nickel(II) Catalyst

An effective shielding of both apical positions of a neutral NiII active site is achieved by dibenzosuberyl groups, both attached via the same donors' N-aryl group in a Cs -type arrangement. The key aniline building block is accessible in a single step from commercially available dibenzosuberol. This shielding approach suppresses chain transfer and branch formation to such an extent that ultrahigh molecular weight polyethylenes (5×106  g mol-1 ) are accessible, with a strictly linear microstructure (<0.1 branches/1000C). Key features of this highly active (4.3×105  turnovers h-1 ) catalyst are an exceptionally facile preparation, thermal robustness (up to 90 °C polymerization temperature), ability for living polymerization and compatibility with THF as a polar reaction medium.

Compartmentalized polymerization in aqueous and organic media to low-entangled ultra high molecular weight polyethylene

Catalytic polymerization in compartmentalized aqueous or non-aqueous media, respectively, with functional-group tolerant Ni(ii) catalysts yields low-entangled UHMWPE.

Towards scalable, low dispersity, and dimensionally tunable 2D platelets using living crystallization-driven self-assembly

Scalable low dispersity platelets were accessed through the self-assembly of crystallizable charge-terminated PFS homopolymers. The use of surfactant counteranions, as well as increasing the self-assembly temperature, improved structure fidelity.

Custom-made polar monomers utilized in nickel and palladium promoted olefin copolymerization

In this review, the functions of custom-made polar monomers are insightfully emphasized in the preparation of functional polyolefins.

Neutral Nickel(II) Catalysts: From Hyperbranched Oligomers to Nanocrystal-Based Materials

Plastics materials are a vital component of modern technologies. They are applied, e.g., in construction, transportation, communication, water supply, or health care. Consequently, polyolefins-the most important plastics by scale-are produced in vast amounts by catalytic polymerization. Effective and selective as the catalysts used may be, their high sensitivity toward any polar compounds limits these methods to hydrocarbon reaction media and monomers like ethylene and propylene, respectively. This can be overcome by less oxophilic late transition metal catalysts, and here particularly neutral nickel(II) catalysts have seen major advances in the past few years. They stand out due to being capable of aqueous catalytic polymerizations. Aqueous polymerizations are benign processes that advantageously yield polymers in the form of particles. Moreover, these catalysts can incorporate polar monomers like acrylates, a realm previously restricted to noble metal catalysts. The introduction of polar moieties can induce properties like compatibility with metals or fibers in high performance composite materials or a desirable degradability.This Account provides a personal account of developments in the past decade. Prior findings are outlined briefly as a background. Aqueous polymerizations afford unique polyethylene morphologies as a result of the unusual underlying particle growth mechanism. Polymer single crystals are formed, which can be composed of a single ultrahigh molecular weight chain. This represents a completely disentangled state of such extremely long polymer chains, which has been long sought-after in order to overcome the difficult processing of high performance ultrahigh molecular weight materials. A key prerequisite for this approach and utilization of these catalysts, in general, is control of polymer branching and molecular weight. This is achieved via remote substituents on the Ni(II)-chelating ligand. Despite their distal position to the active site, weak secondary interactions control whether branching and chain transfer pathways compete very effectively with chain growth or are suppressed entirely. This provides access to hyperbranched oligomers, on the one hand, and enables living polymerizations to strictly linear high molecular weight polymer, on the other hand. Other advanced catalysts provide linear copolymers with in-chain polar monomer repeat units for the first time with non-noble metal active sites. Mechanistic studies further revealed that for copolymerizations with polar vinyl monomers the decisive limiting factor is irreversible termination reactions with neutral Ni(II) catalysts, rather than the well-recognized reversible blocking of coordination sites by the polar functional groups found for other types of catalysts. The mechanistic picture also implies the possibility of free-radical pathways, and their role in the formation of desirable polymer end groups and polymer blends is now being recognized. The area of neutral Ni(II) catalysts has progressed significantly in the entire range from fundamental mechanistic understanding, catalyst performance, and previously inaccessible polymer microstructures, and it is moving forward to materials through unique concepts. The unprecedented ability to incorporate functional groups into linear crystalline polyethylene also provides perspectives for much needed polyolefin materials that will not persist in the natural environment for several decades but that can be degraded by virtue of low levels of functional groups.