Interlocking Matrix and Filler for Enhanced Individualization and Reinforcement in Polymer-Single-Walled Carbon Nanotube Composites

Poor individualization and interfacial adhesion prevent single-walled carbon nanotube (SWNT)-polymer composites from reaching outstanding mechanical properties. With much larger diameters, but common structural features (high aspect ratio and absence of functional groups for covalent or supramolecular attachment with the polymer), carbon fibers face similar problems, which are addressed by covering the fibers with a thin layer of polymer. This sizing strategy has allowed carbon fibers to become the filler of choice for the highest performing materials. Inspired by this, here we investigate the use of the mechanical bond to wrap SWNTs with a layer of polymeric material to produce SWNTs mechanically interlocked with a layer of polymer. We first validate the formation of mechanically interlocked nanotubes (MINTs) using mixtures of SWNTs of relatively large average diameter (1.6 ± 0.4 nm), which are commercially available at reasonable prices and therefore could be technologically relevant as polymer fillers. We then design and synthesize by ring-opening metathesis polymerization (ROMP) a polymer decorated with multiple U-shaped molecules, which are later ring-closed around the SWNTs using metathesis. The obtained hybrids contain a high degree of individualized SWNTs and exhibit significantly increased mechanical properties when compared to the matrix polymer. We envision that this strategy could be employed to produce SWNTs interlocked with polymer layers with various designs for polymer reinforcement.

Multiple applications of polymers containing electron-reservoir metal-sandwich complexes

Ferrocene-containing polymers have been investigated for more than six decades, and more recently modern synthetic methods have allowed the fabrication of precise polymers that contain a variety of transition-metal complexes. Trends are now oriented towards applications, such as optics, energy conversion and storage, electrochemistry, magnetics, electric conductors and biomedicine. Metal-sandwich complexes such as those of ferrocene type and other related complexes that present redox-robust groups in polymers, i.e. that are isolable in both their oxidized and reduced forms, are of particular interest, because it is possible to address them using electronic or photonic redox stimuli for application. Our research groups have called such complexes Electron-Reservoirs and introduced them in the main chain or in the side chains of well-defined polymers. For instance, polymers with ferrocene in the main chain or in the side chain are oxidized to stable polycationic polyelectrolytes only if ferrocene is part of a biferrocene unit, because biferrocene oxidation leads to the biferrocenium cation that is stabilized by the mixed valency. Then a group of several redox-robust iron sandwich complexes were fabricated and incorporated in precise polymers including multi-block copolymers whose controlled synthesis and block incorporation was achieved for instance using ring-opening-metathesis polymerization. Applications of this family of Electron-Reservoir-containing polymers includes electrochemically induced derivatization of electrodes by decorating them with these polymers, molecular recognition and redox sensing, electrochromics with multiple colours, generation of gold and silver nanoparticles of various size by reduction of gold(iii) and silver(i) precursors and their use for nanocatalysis towards depollution and biomedicine.

'Click' conjugated porous polymer nanofilm with a large domain size created by a liquid/liquid interfacial protocol

A liquid/liquid interfacial method is used to synthesize a conjugated porous polymer nanofilm with a large domain size. Copper-catalyzed azide-alkyne cycloaddition between a triangular terminal alkyne and azide monomers at a water/dichloromethane interface generates a 1,2,3-triazole-linked polymer nanofilm featuring a large aspect ratio and robustness against heat and pH.

Stronger aramids through molecular design and nanoprocessing

We describe how to build ultrastrong polymeric nanofilms through a combination of molecular design and nanostructuration.

Click Co sandwich-terminated dendrimers as polyhydride reservoirs and micellar templates

Neutral click metallodendrimers with [Co^I(η⁴-cyclopentadiene)(η⁵-cyclopentadienyl)] termini are synthesized by reduction of dendrimers with 9, 27 or 81 cobalticenium termini and serve as polyhydride reservoirs and reductants; for instance, they reduce proton sources to H₂ and Au^III to micellized capsules of gold nanoparticles.

Liquid/Liquid Interfacial Synthesis of a Click Nanosheet

A liquid/liquid interfacial synthesis is employed, for the first time, to synthesize a covalent two-dimensional polymer nanosheet. Copper-catalyzed azide-alkyne cycloaddition (CuAAC) between a three-way terminal alkyne and azide at a water/dichloromethane interface generates a 1,2,3-triazole-linked nanosheet. The resultant nanosheet, with a flat and smooth texture, has a maximum domain size of 20 μm and minimum thickness of 5.3 nm. The starting monomers in the organic phase and the copper catalyst in the aqueous phase can only meet at the liquid/liquid interface as a two-dimensional reaction space; this allows them to form the two-dimensional polymer. The robust triazole linkage generated by irreversible covalent-bond formation allows the nanosheet to resist hydrolysis under both acidic and alkaline conditions, and to endure pyrolysis up to more than 300 °C. The coordination ability of the triazolyl group enables the nanosheet to act as a reservoir for metal ions, with an affinity order of Pd²⁺ >Au³⁺ >Cu²⁺ .

Synthesis and redox activity of "clicked" triazolylbiferrocenyl polymers, network encapsulation of gold and silver nanoparticles and anion sensing

The design of redox-robust polymers is called for in view of interactions with nanoparticles and surfaces toward applications in nanonetwork design, sensing, and catalysis. Redox-robust triazolylbiferrocenyl (trzBiFc) polymers have been synthesized with the organometallic group in the side chain by ring-opening metathesis polymerization using Grubbs-III catalyst or radical polymerization and with the organometallic group in the main chain by Cu(I) azide alkyne cycloaddition (CuAAC) catalyzed by [Cu(I)(hexabenzyltren)]Br. Oxidation of the trzBiFc polymers with ferricenium hexafluorophosphate yields the stable 35-electron class-II mixed-valent biferrocenium polymer. Oxidation of these polymers with Au(III) or Ag(I) gives nanosnake-shaped networks (observed by transmission electron microscopy and atomic force microscopy) of this mixed-valent Fe(II)Fe(III) polymer with encapsulated metal nanoparticles (NPs) when the organoiron group is located on the side chain. The factors that are suggested to be synergistically responsible for the NP stabilization and network formation are the polymer bulk, the trz coordination, the nearby cationic charge of trzBiFc, and the inter-BiFc distance. For instance, reduction of such an oxidized trzBiFc-AuNP polymer to the neutral trzBiFc-AuNP polymer with NaBH4 destroys the network, and the product flocculates. The polymers easily provide modified electrodes that sense, via the oxidized Fe(II)Fe(III) and Fe(III)Fe(III) polymer states, respectively, ATP(2-) via the outer ferrocenyl units of the polymer and Pd(II) via the inner Fc units; this recognition works well in dichloromethane, but also to a lesser extent in water with NaCl as the electrolyte.

Mixed-valent click intertwined polymer units containing biferrocenium chloride side chains form nanosnakes that encapsulate gold nanoparticles

Polymers containing triazolylbiferrocene are synthesized by ROMP or radical chain reactions and react with HAuCl4 to provide class-2 mixed-valent triazolylbiferrocenium polyelectrolyte networks (observed inter alia by TEM and AFM) that encapsulate gold nanoparticles (AuNPs). With triazolylbiferrocenium in the side polymer chain, the intertwined polymer networks form nanosnakes, unlike with triazolylbiferrocenium in the main polymer chain. By contrast, simple ferrocene-containing polymers do not form such a ferricenium network upon reaction with Au(III), but only small AuNPs, showing that the triazolyl ligand, the cationic charge, and the biferrocenium structure are coresponsible for such network formations.

Metalation of polyamine dendrimers with ethynylcobalticenium for the construction of mono- and heterobimetallic polycationic metallodendrimers

The introduction of robust redox groups at the periphery of common amine-terminated dendrimers is of interest in the design of dendritic nanobatteries, sensors, and redox catalysts. Here we are applying the recently discovered uncatalyzed hydroamination of ethynylcobalticenium, a mild "green" reaction that quantitatively yields trans-enamines without the formation of any byproduct, to functionalize dendrimers that are terminated with primary or secondary amino groups. Poly(amido amine) (PAMAM) dendrimers terminated by primary amino groups and arene-centered dendrimers terminated by secondary amino groups yield dendrimers that contain up to 81 trans-enamine-cobalticenium termini using this reaction. The hydroamination reaction was also conducted with dendrimers that contained ferrocenylmethylamino groups, which yielded dendrimers that contained both ferrocenyl and cobalticenium termini. The size of the dendrimers was investigated using both dynamic light scattering and diffusion-ordered spectroscopy (DOSY) (1)H NMR spectroscopy, and the number of electrons involved in heterogeneous multielectron transfers at electrodes was searched by cyclic voltammetry. The latter works well up to the 27-branch dendrimer, whereas the 81-dendrimer yielded a result in an excess amount (110 electrons) owing to adsorption onto the cathode that becomes all the more significant as the metallodendrimer size increases.

Click dendrimers and triazole-related aspects: catalysts, mechanism, synthesis, and functions. A bridge between dendritic architectures and nanomaterials

One of the primary recent improvements in molecular chemistry is the now decade-old concept of click chemistry. Typically performed as copper-catalyzed azide-alkyne (CuAAC) Huisgen-type 1,3-cycloadditions, this reaction has many applications in biomedicine and materials science. The application of this chemistry in dendrimer synthesis beyond the zeroth generation and in nanoparticle functionalization requires stoichiometric use of the most common click catalyst, CuSO(4)·5H(2)O with sodium ascorbate. Efforts to develop milder reaction conditions for these substrates have led to the design of polydentate nitrogen ligands. Along these lines, we have described a new, efficient, practical, and easy-to-synthesize catalytic complex, [Cu(I)(hexabenzyltren)]Br, 1 [tren = tris(2-aminoethyl)amine], for the synthesis of relatively large dendrimers and functional gold nanoparticles (AuNPs). This efficient catalyst can be used alone in 0.1% mol amounts for nondendritic click reactions or with the sodium-ascorbate additive, which inhibits aerobic catalyst oxidation. Alternatively, catalytic quantities of the air-stable compounds hexabenzyltren and CuBr added to the click reaction medium can provide analogously satisfactory results. Based on this catalyst as a core, we have also designed and synthesized analogous Cu(I)-centered dendritic catalysts that are much less air-sensitive than 1 and are soluble in organic solvents or in water (depending on the nature of the terminal groups). These multivalent catalysts facilitate efficient click chemistry and exert positive dendritic effects that mimic enzyme activity. We propose a monometallic CuAAC click mechanism for this process. Although the primary use of click chemistry with dendrimers has been to decorate dendrimers with a large number of molecules for medicinal or materials purposes, we are specifically interested in the formation of intradendritic [1,2,3]-triazole heterocycles that coordinate to transition-metal ions via their nitrogen atoms. We describe applications including molecular recognition of anions and cations and the stabilization of transition metal nanoparticles according to a principle pioneered by Crooks with poly(amido amine) (PAMAM) dendrimers, and in particular, the control of structural and reactivity parameters in which the intradendritic [1,2,3]-triazoles and peripheral tripodal tri(ethylene glycol) termini play key roles in the click-dendrimer mediated synthesis and stabilization of gold nanoparticles (AuNPs). By varying these parameters, we have stabilized water-soluble, weakly liganded AuNPs between 1.8 and 50 nm in size and have shown large differences in behavior between AuNPs and PdNPs. Overall, the new catalyst design and the possibilities of click dendrimer chemistry introduce a bridge between dendritic architectures and the world of nanomaterials for multiple applications.