This in-depth review covers progress in the area of polyferrocenylsilanes (PFS), a well-established, readily accessible class of main chain organosilicon metallopolymer consisting of alternating ferrocene and organosilane units. Soluble, high molar mass samples of these materials were first prepared in the early 1990s by ring-opening polymerisation (ROP) of silicon-bridged [1]ferrocenophanes (sila[1]ferrocenophanes). Thermal, transition metal-catalysed, and also two different living anionic ROP methodologies have been developed: the latter permit access to controlled polymer architectures, such as monodisperse PFS homopolymers and block copolymers. Depending on the substituents, PFS homopolymers can be amorphous or crystalline, and soluble in organic solvents or aqueous media. PFS materials have attracted widespread attention as high refractive index materials, electroactuated redox-active gels, fibres, films, and nanoporous membranes, as precursors to nanostructured magnetic ceramics, and as etch resists to plasmas and other radiation. PFS block copolymers form phase-separated iron-rich, redox-active and preceramic nanodomains in the solid state with applications in nanolithography, nanotemplating, and nanocatalysis. In selective solvents functional micelles with core-shell structures are formed. Block copolymers with a crystallisable PFS core-forming block were the first to be found to undergo "living crystallisation-driven self-assembly" in solution, a controlled method of assembling block copolymers into 1D or 2D structures that resembles a living covalent polymerisation, but on a longer length scale of 10 nm-10 μm.
Self-assembled 1D block copolymer nanoparticles (micelles) are of interest for a range of applications. However, morphologically pure samples are often challenging to access, and precise dimensional control is not possible. Moreover, the development of synthetic protocols that operate on a commercially viable scale has been a major challenge. Herein, we describe the preparation 1D fiber-like micelles with crystalline cores at high concentrations by a one-pot process termed polymerization-induced crystallization-driven self-assembly (PI-CDSA). We also demonstrate the formation of uniform fibers by living PI-CDSA, a process in which block copolymer synthesis, self-assembly, and seeded growth are combined. We have demonstrated that the method is successful for block copolymers that possess the same composition as that of the seed (homoepitaxial growth) and also where the coronal chemistries differ to give segmented 1D fibers known as block co-micelles. We have also shown that heteroepitaxial growth allows the formation of scaled-up block co-micelles where the composition of both the core and corona was varied. These proof-of-concept experiments indicate that PI-CDSA is a promising, scalable route to a variety of polydisperse or uniform 1D nanoparticles based on block copolymers with different crystalline core chemistries and, therefore, functions.
There is a broad interest in elongated colloids as drug delivery vehicles, and current research aims to address how their length and aspect ratio affect interactions with cells. Block copolymer (BCP) micelles offer the opportunity to vary micelle length while maintaining cross-sectional width with corona chains that maintain a common surface chemistry across these structures. However, most elongated BCP micelles used in cell studies are characterized by a very broad length distribution. Here, we describe the synthesis and self-assembly properties of a diblock copolymer with a polyferrocenylsilane core-forming block and a corona block consisting of a statistical polymer of (aminopropyl)methacrylamide and oligo(ethylene glycol methacrylate) (M = 500) (PFS27-b-PAPMA3-stat-OEGMA48). Self-assembly in water gave a mixture of structures including rodlike micelles. In alcohols, different types of structures were obtained depending on the alcohol employed (butanol, 2-propanol, ethanol, and methanol). In ethanol, the polymer formed long micelles of uniform width by crystallization-driven self-assembly. Following sonication, a series of rodlike micelles with different lengths (80 to 2000 nm) and narrow length distributions (L w/L n < 1.10) were generated by seeded growth. These micelles could be transferred to aqueous media and maintained colloidally stable in PBS (phosphate-buffered saline) buffer for more than three months. In these micelles, the POEGMA brush provides a “stealth” coating to minimize the interaction with proteins and cells, and the APMA groups provide functionality for attachment of drugs or metal chelators for potential therapeutic applications. Studies in two human breast cancer cell lines (MDA-MB-231 and MDA-MB-436) show no signs of toxicity for micelle concentrations up to 0.1 mg·mL–1. We also show that metal chelators can be covalently attached to the amino groups in the corona and labeled with heavy metals, opening the door to future experiments with radionuclides.
This paper reports a new synthetic strategy for the preparation of polyferrocenylsilane (PFS) block copolymers. The block copolymers were prepared by Cu-catalyzed alkyne/azide cycloaddition of two homopolymer precursors that allows access to new functional PFS block copolymers (e.g., polyferrocenylsilane-block-poly(N-isopropylacrylamide)) (PFS-b-PNIPAM)). Trimethylsilyl-protected, alkyne-terminated PFS homopolymer was first prepared via living anionic polymerization, terminating living PFS with commercially available 4-[(trimethylsilyl)ethynyl]benzaldehyde. Subsequent deprotection of the trimethylsilyl group with NaOMe yielded the ethynyl-terminated PFS (ω-alkyne-PFS). This method should be readily applicable to other polymers prepared by living anionic polymerization. Subsequently, non-PFS homopolymers containing a complementary "clickable" azide functional group were synthesized either by anionic polymerization, modification of a commercially available polymer, or atom transfer radical polymerization via two different approaches. In an azide postpolymerization modification approach, polystyrene (PS) and poly(methyl methacrylate) (PMMA) were functionalized by azide substitution of the terminal halide after ATRP. Alternatively, the azide moiety was incorporated into the ATRP initiator prior to polymerization, e.g., to give PNIPAM-N 3 and poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA-N 3 ). Finally, the alkyne-terminated PFS segment and the azide functionalized counter block were coupled through the formation of a 1,2,3triazole ring. In this report, PFS-b-PNIPAM, PFS-b-PDMAEMA, PFS-b-PS, PFS-b-PMMA, PFS-b-polydimethylsiloxane, and PFS-block-poly(ethylene oxide) have been synthesized via this convenient modular protocol in high yield and high purity.
Toroidal nanostructures are of growing importance due to their unique geometry and potential utility in materials fabrication. Although a variety of amphiphilic block copolymers have been shown to selfassemble into toroidal micelles, the conventional methods used are often very slow with little control over the size of the resulting nanostructures. Here, we report a rapid and efficient synthetic route to prepare toroidal micelles of near uniform diameter through the cooperative co-assembly of amorphous blends of polyferrocenylsilane block copolymer and homopolymer, where the degree of polymerization of the core-forming metalloblock in the former is greater than for the latter. The selfassembly process is accomplished within a few minutes and the ring size of the toroids can be varied between 30 and 90 nm by adjusting the mass ratio of the block copolymer and homopolymer. The kinetic stability of the resulting toroidal micelles can be enhanced by frustrating core crystallization through solvent modulation and the toroids can also be readily used as templates to fabricate circular arrays of metal nanoparticles.
General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. TECHNIQUESUnless otherwise stated, all reactions were carried out on an all-glass vacuum line under nitrogen or in anMBraun glovebox under an inert purified nitrogen atmosphere.
We report experiments on the aging of monodisperse wet microfoams. We use the flow focusing technique to produce perfectly monodisperse microbubbles from 50 to 80 μm in diameter. This results in a foam of spherical bubbles of the same size ordered in random ordered lattices like “crystal grains” above the foam/liquid interface. We observe two different behaviors while the foam drains without any interference. At early times, the foam bubble size is almost constant from 10 to 20 min depending on the initial diameter of the bubbles. For longer times, the foam reaches a scaling state where the bubbles mean diameter growth agrees with the theoretical prediction t1/3.
General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. [a] Vincent T. Annibale, [a] Natalie E. Pridmore, [a] Alex M. Oliver, [a] and Ian Manners* [a] Abstract: We report the addition of a cyclotriphosphine to a broad range of nitriles giving access to the first examples of free 1-aza-2,3,4-triphospholenes in a rapid, ambient temperature, one-pot, high-yield protocol. The reaction produces electron-rich heterocycles (four lone pairs) and features homoatomic -bond heterolysis, thereby combining the key features of the 1,3-dipolar cycloaddition chemistry of azides and cyclopropanes. We also report the first catalytic addition of P-P bonds to the CN triple bond. The coordination chemistry of the new heterocycles is explored.
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