Shaped ceramics with tunable magnetic properties from metal-containing polymers

Ian Manners (1961-2023): Learning to Fly

Ian Manners, an internationally renowned main-group and materials scientist, passed away on December 3, 2023. He will be remembered as a brilliant researcher, an avid birdwatching enthusiast, Pink Floyd fan, and champion of his students who had a profoundly positive impact on those around him.

Stimuli-Driven Insulator-Conductor Transition in a Flexible Polymer Composite Enabled by Biphasic Liquid Metal

Metal-polymer composites (MPCs) with combined properties of metals and polymers have achieved much industrial success. However, metals in MPCs are thought to be ordinary and invariable electrically conductive fillers in supportive polymers to show limited use in modern technologies. This work that is disclosed here, for the first time, introduces stimuli-driven transition from biphasic to monophasic state of liquid metal into polymer science to form dynamic soft conductors from the binary metal-polymer composites. The binary metal that exhibits temperature-driven reversible transition between solid and liquid states via a biphasic state is fabricated. A conducting stretchable polymer composite is developed using the judiciously chosen biphasic binary metal that undergoes conductor to insulator transition upon stretching. Insulating stretched films become conducting upon heating. A "tube" model elegantly describes such distinctive deformation/temperature-dependent behaviors. Moreover, the conducting polymer composite shows decrease in its resistance upon increasing the sample temperature. The resistance can be tuned from 1 to 10⁸  Ω depending on the state of binary metal in the phase diagram. This work would build the intimate and interesting connection between metal phases and polymer science toward next-generation soft conductors and beyond.

Ordered Mesoporous Silica Pyrolyzed from Single-Source Self-Assembled Organic-Inorganic Giant Surfactants

We report the preparation of hexagonal mesoporous silica from single-source giant surfactants constructed via dihydroxyl-functionlized polyhedral oligomeric silsesquioxane (DPOSS) heads and a polystyrene (PS) tail. After thermal annealing, the obtained well-ordered hexagonal hybrid was pyrolyzed to afford well-ordered mesoporous silica. A high porosity (e.g., 581 m²/g) and a uniform and narrow pore size distribution (e.g., 3.3 nm) were achieved. Mesoporous silica in diverse shapes and morphologies were achieved by processing the precursor. When the PS tail length was increased, the pore size expanded accordingly. Moreover, such pyrolyzed, ordered mesoporous silica can help to increase both efficiency and stability of nanocatalysts.

Superparamagnetic Silicon Carbonitride Ceramic Fibers Through In Situ Generation of Iron Silicide Nanoparticles During Pyrolysis of an Iron-Modified Polysilazane

Ceramic fibers are high-tech structural key components of ceramic matrix composites (CMCs), which are a very promising class of materials for applications in next-generation turbines, especially nonoxide ceramic fibers, usually produced by the polymer-derived ceramics (PDC) route, which possess the enhanced mechanical and thermostructural properties necessary to withstand the harsh conditions (temperature and atmosphere) imposed on CMCs. However, recycling composite materials, such as fiber-reinforced polymers and CMCs, is still a big challenge. Here, we present for the first time the processing of superparamagnetic iron-containing ceramic fibers, which, due to their magnetic properties, can be separated from the matrix material of a composite. The synthesis strategy of the novel functional ceramic fibers is based on a tailored reaction of polyorganosilazane with an iron complex, resulting in a suitable, meltable polymer. After melt-spinning and curing, subsequent pyrolysis leads to superparamagnetic ceramic fibers with a saturation magnetization of 1.54 emu g^-1 because of in situ-formed iron silicide nanoparticles of an average size of 7.5 nm, homogeneously dispersed in an amorphous SiCNO matrix. Moreover, the ceramic fibers exhibit a tensile strength of 1.24 GPa and appropriate oxidation resistance. The developed versatile reaction strategy allows also for the incorporation of other elements to implement further functionalities for processing of multifunctional composites.

Ring-Opening Polymerisation of Low-Strain Nickelocenophanes: Synthesis and Magnetic Properties of Polynickelocenes with Carbon and Silicon Main Chain Spacers

Polymetallocenes based on ferrocene, and to a lesser extent cobaltocene, have been well-studied, whereas analogous systems based on nickelocene are virtually unexplored. It has been previously shown that poly(nickelocenylpropylene) [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₃ ]_n is formed as a mixture of cyclic (6_x ) and linear (7) components by the reversible ring-opening polymerisation (ROP) of tricarba[3]nickelocenophane [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₃ ] (5). Herein the generality of this approach to main-chain polynickelocenes is demonstrated and the ROP of tetracarba[4]nickelocenophane [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₄ ] (8), and disila[2]nickelocenophane [Ni(η⁵ -C₅ H₄ )₂ (SiMe₂ )₂ ] (12) is described, to yield predominantly insoluble homopolymers poly(nickelocenylbutylene) [Ni(η⁵ -C₅ H₄ )₂ (CH₂ )₄ ]_n (13) and poly(tetramethyldisilylnickelocene) [Ni(η⁵ -C₅ H₄ )₂ (SiMe₂ )₂ ]_n (14), respectively. The ROP of 8 and 12 was also found to be reversible at elevated temperature. To access soluble high molar mass materials, copolymerisations of 5, 8, and 12 were performed. Superconducting quantum interference device (SQUID) magnetometry measurements of 13 and 14 indicated that these homopolymers behave as simple paramagnets at temperatures greater than 50 K, with significant antiferromagnetic coupling that is notably larger in carbon-bridged 6_x /7 and 13 compared to the disilyl-bridged 14. However, the behaviour of these polynickelocenes deviates substantially from the Curie-Weiss law at low temperatures due to considerable zero-field splitting.

Synthesis, thin-film self-assembly, and pyrolysis of ruthenium-containing polyferrocenylsilane block copolymers

The self-assembly of a ruthenium-containing polyferrocenylsilane in bulk and thin films yielded spherical or cylindrical domains in a PS matrix; pyrolysis provided a route to bimetallic Fe/Ru NPs for potential catalytic applications.

Synthesis of Coordination Polymer Nanoparticles using Self-Assembled Block Copolymers as Template

Nowadays there is a high demand in specialized functional materials, for example, for applications as sensors in biomedicine. For the realization of such applications, nanostructures and the integration in a composite matrix are indispensable. Coordination polymers and networks, for example, with spin crossover properties, are a highly promising family of switchable materials in which the switching process can be triggered by various external stimuli. An overview over different strategies for the synthesis of nanoparticles of such systems is given. A special focus is set on the use of block copolymer micelles as templates for the synthesis of nanocomposites. The block copolymer defines the final size and shape of the nanoparticle core. Additionally it allows a further functionalization of the obtained nanoparticles by variation of the polymer blocks and an easy deposition of the composite material on surfaces.

Tunable room-temperature soft ferromagnetism in magnetoceramics of organometallic dendrimers

This article represents an introduction of new dendrimeric precursors to magnetic ceramics, and homometallic and heterometallic dendrimers with tunable magnetic properties.

Synthesis, characterization, thermal properties and antiproliferative potential of copper(II) 4'-phenyl-terpyridine compounds

Reactions between 4'-phenyl-terpyridine (L) and several Cu(II) salts (p-toluenesulfonate, benzoate and o-, m- or p-hydroxybenzoate) led to the formation of [Cu(p-SO3C6H4CH3)L(H2O)2](p-SO3C6H4CH3) (1), [Cu(OCOPh)2L] (2), [Cu(o-OCOC6H4OH)2L] (3), [Cu(m-OCOC6H4OH)2L]4·MeOH (·MeOH) and [Cu(p-OCOC6H4OH)2L]5·2H2O (·2H2O), which were characterized by elemental and TG-DTA analyses, ESI-MS, IR spectroscopy and single crystal X-ray diffraction, as well as by conductivimetry. In all structures the Cu atoms present N3O3 octahedral coordination geometries, which, in 2-5, are highly distorted as a result of the chelating-bidentate mode of one of the carboxylate ligands. Intermolecular π···π stacking interactions could also be found in 2-5 (in the 3.569-3.651 Å range and involving solely the pyridyl rings). Medium-strong hydrogen bond interactions lead to infinite 1D chains (in 1 and 4) and to an infinite 2D network (in 5). Compounds 1 and 4 show high in vitro cytotoxicity towards HCT116 colorectal carcinoma and HepG2 hepatocellular carcinoma cell lines. The antiproliferative potential of compound 1 is due to an increase of the apoptotic process that was confirmed by Hoechst staining, flow cytometry and RT-qPCR. All compounds able to non-covalently intercalate the DNA helix and induce in vitro pDNA double-strand breaks in the absence of H2O2. Concerning compound 1, the hydroxyl radical and singlet oxygen do not appear to be involved in the pDNA cleavage process and the fact that this cleavage also occurs in the absence of molecular oxygen points to a hydrolytic mechanism of cleavage.

Polyferrocenylsilanes: synthesis, properties, and applications

This comprehensive review covers polyferrocenylsilanes (PFSs), a well-established, readily accessible class of main chain organosilicon metallopolymer. The focus is on the recent advances involving PFS homopolymers and block copolymers and the article covers the synthesis, properties, and applications of these fascinating materials.

Functional Materials Based on Metal-Containing Polymers

Since the dawn of human civilization, there has been a demand for materials that include ceramics, metals, and polymers. Increasing demand as well as the need for enhanced performance has driven material scientists to research metal-containing polymers as complements of these materials. Consequently, metal-containing polymers that integrate the excellent thermal, electronic, optical, and magnetic properties of metals with the lightweight, low cost, and in some cases, the chemical stability of organic-based polymers have been designed, and used as catalysts, sensors, ceramic precursors, magnetic materials, and electrical conductors. This chapter provides an overview of some of these functional metal-containing polymers.

f-Block Ansa Complexes in the Solid State: [3]Thoro- and [3]Uranocenophanes

The preparation of [3]thoro- and [3]uranocenophanes, the first structurally authenticated ansa-bridged complexes of actinocenes, is reported. Following a flytrap route, 1,2-bis(cyclooctatetraenyldimethylsilyl)methane was synthesized, reduced to its tetraanion, and subsequently converted into bridged uranocene and thorocene complexes by salt metathesis with the corresponding actinide tetrachlorides. In addition, their electronic structures have been investigated by experimental (UV/Vis spectroscopy, cyclic voltammetry) and theoretical (DFT) methods.

Redox-responsive organometallic hydrogels for in situ metal nanoparticle synthesis

A new class of redox active hydrogels composed of poly(ferrocenylsilane) polyanion and poly(ethylene glycol) chains was assembled, using a copper-free azide-alkyne Huisgen cycloaddition reaction. These organometallic hydrogels displayed reversible collapse and reswelling upon chemical oxidation and reduction, respectively, and formed relatively well-defined, unaggregated Pd(0) nanoparticles (8.2 ± 2.2 nm) from K2PdCl4 salts.

Combination of magnetic and enhanced mechanical properties for copolymer-grafted magnetite composite thermoplastic elastomers

Composite thermoplastic elastomers (CTPEs) of magnetic copolymer-grafted nanoparticles (magnetite, Fe3O4) were synthesized and characterized to generate magnetic CTPEs, which combined the magnetic property of Fe3O4 nanoparticles and the thermoplastic elasticity of the grafted amorphous polymer matrix. Fe3O4 nanoparticles served as stiff, multiple physical cross-linking points homogeneously dispersed in the grafted poly(n-butyl acrylate-co-methyl methacrylate) rubbery matrix synthesized via the activators regenerated by electron transfer for atom transfer radical polymerization method (ARGET ATRP). The preparation technique for magnetic CTPEs opened a new route toward developing a wide spectrum of magnetic elastomeric materials with strongly enhanced macroscopic properties. Differential scanning calorimetry (DSC) was used to measure the glass transition temperatures, and thermogravimetric analysis (TGA) was used to examine thermal stabilities of these CTPEs. The magnetic property could be conveniently tuned by adjusting the content of Fe3O4 nanoparticles in CTPEs. Compared to their linear copolymers, these magnetic CTPEs showed significant increases in tensile strength and elastic recovery. In situ small-angle X-ray scattering measurement was conducted to reveal the microstructural evolution of CTPEs during tensile deformation.

Ceramic Nanocomposites from Tailor-Made Preceramic Polymers

The present Review addresses current developments related to polymer-derived ceramic nanocomposites (PDC-NCs). Different classes of preceramic polymers are briefly introduced and their conversion into ceramic materials with adjustable phase compositions and microstructures is presented. Emphasis is set on discussing the intimate relationship between the chemistry and structural architecture of the precursor and the structural features and properties of the resulting ceramic nanocomposites. Various structural and functional properties of silicon-containing ceramic nanocomposites as well as different preparative strategies to achieve nano-scaled PDC-NC-based ordered structures are highlighted, based on selected ceramic nanocomposite systems. Furthermore, prospective applications of the PDC-NCs such as high-temperature stable materials for thermal protection systems, membranes for hot gas separation purposes, materials for heterogeneous catalysis, nano-confinement materials for hydrogen storage applications as well as anode materials for secondary ion batteries are introduced and discussed in detail.

Synthesis of main-chain metal carbonyl organometallic macromolecules (MCMCOMs)

Synthesis of main-chain metal carbonyl organometallic macromolecules (MCMCOMs) is difficult, mainly due to the instability of metal carbonyl complexes. Despite its challenge a number of MCMCOMs has been prepared by strategically using organometallic, organic, and polymer synthetic chemistry. Main contributions to this research field were reported by the groups of Tyler, Pannell, and Wang and are briefly summarized in this article.

Highly-metallized phosphonium polyelectrolytes

The synthesis, characterization, and pyrolysis of a novel class of highly-metallized, redox-active polyelectrolytes that employ phosphorus as a scaffold for the installation of transition metals is described.

Magnetoceramics from the bulk pyrolysis of polysilazane cross-linked by polyferrocenylcarbosilanes with hyperbranched topology

In this contribution, we report a novel strategy for the synthesis of nanocrystal-containing magnetoceramics with an ultralow hysteresis loss by the pyrolysis of commercial polysilazane cross-linked with a functional metallopolymer possessing hyperbranched topology. The usage of hyperbranched polyferrocenylcarbosilane offers either enhanced ceramic yield or magnetic functionality of pyrolyzed ceramics. The ceramic yield was enhanced accompanied by a decreased evolution of hydrocarbons and NH3 because of the cross-linking of precursors and the hyperbranched cross-linker. The nucleation of Fe5Si3 from the reaction of iron atoms with Si-C-N amorphous phase promoted the formation of α-Si3N4 and SiC crystals. After annealing at 1300 °C, stable Fe3Si crystals were generated from the transformation of the metastable Fe5Si3 phase. The nanocrystal-containing ceramics showed good ferromagnetism with an ultralow (close to 0) hysteresis loss. This method is convenient for the generation of tunable functional ceramics using a commercial polymeric precursor cross-linked by a metallopolymer with a designed topology.

Facile preparation of cobaltocenium-containing polyelectrolyte via click chemistry and RAFT polymerization

A facile method to prepare cationic cobaltocenium-containing polyelectrolyte is reported. Cobaltocenium monomer with methacrylate is synthesized by copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction between 2-azidoethyl methacrylate and ethynylcobaltocenium hexafluorophosphate. Further controlled polymerization is achieved by reversible addition-fragmentation chain transfer polymerization (RAFT) by using cumyl dithiobenzoate (CDB) as a chain transfer agent. Kinetic study demonstrates the controlled/living process of polymerization. The obtained side-chain cobaltocenium-containing polymer is a metal-containing polyelectrolyte that shows characteristic redox behavior of cobaltocenium.

Synthesis and structure of distanna and tristanna ansa half-sandwich complexes of ruthenium and nickel

The synthesis and structural characterization of the first tin-bridged ansa half-sandwich complexes via a two-step protocol from Na[η(5)-C(5)H(5)Ru(CO)(2)] and in situ generated Na[η(5)-C(5)H(5)Ni(CO)] are presented. Both compounds are characterized by multinuclear NMR spectroscopy and single-crystal diffraction.