Topologies core-shell

In this work we present hyperbranched polymers as platforms for catalysts that fall into three major classes, according to their topology and binding mode to the polymeric support (Fig. 2) (i) defined multiple site catalysts (ii) dendritic core-shell catalysts (iii) supramolecular catalyst complexes. 

For systems presenting a type of supramolecular Darwinism, see Muller A et al (2001) Generation of cluster capsules (I-h) from decomposition products of a smaller cluster (Keggin-T-d) while surviving ones get encapsulated species with core-shell topology formed by a fundamental symmetry-driven reaction. Chem Commun 657-658... 

After the initial reports on dendritic molecules [19], proposals have been made for the construction and applications of guest-host systems made out of dendrimers [1,2,35]. The concept of topological trapping by core-shell molecules is based on... 

As for the linear properties, numerous approaches have been proposed to predict and explain the nonlinear optical response of nanocomposite materials beyond the hypothesis leading to the simple model presented above ( 3.2.2). Especially, Eq. (27) does not hold as soon as metal concentration is large and, a fortiori, reaches the percolation threshold. Several EMT or topological methods have then been developed to account for such regimes and for different types of material morphology, using different calculation methods [38, 81, 83, 88, 96-116]. Let us mention works devoted to ellipsoidal [99, 100, 109] or cylindrical [97] inclusions, effect of a shape distribution [110, 115], core-shell particles [114, 116], layered composites [103], nonlinear inclusions in a nonlinear host medium [88], linear inclusions in a nonlinear host medium [108], percolated media and fractals [101, 104-106, 108]. Attempts to simulate in a nonlinear EMT the influence of temperature have also been reported [107, 113]. 

Keywords. Nanocrystals, Core-shell particles. Topology, Opals, Capsules, Surface plasmon absorption, Bragg diffraction. Arrays, Colloidal crystals... 

In Fig. 6, we illustrate some different ways that the core-shell topology could be varied for silica and gold. So far we have considered the two normal core-shell structures. We now focus on the third example the assembly of Au Si02 nanoparticles onto spherical polystyrene latex colloids. The resulting spheres are also essentially different to continuous metal shells grown on colloid templates, which have been reported by Halas and colleagues [17] and by van Blaaderen and coworkers [18]. Such continuous shells display optical properties associated with resonances of the whole shell, and are therefore extremely sensitive to both core size and shell thickness, while in the system presented here... 

Fig. 6. Three ways to construct silica-gold core shell particles of different topology...

Fig. 13.11 Hyperbranched polyglycidol as a molecular nanoparticle, with its core/shell topology.

The topology of molecules can drastically influence their supramolecular chemistries and properties in general. For example, dendrimers or hyperbranched polymers show dramatically different properties when compared with their linear counterparts. To take a recent example, hyperbranched polyglycerols with a core-shell amphiphile structure encapsulate guests and thereby act as phase-transfer agents, while their strictly linear countei-parts do not.f i... 

Recent advances in polymer chemistry, in particular, in controlled radical polymerization, have enabled the synthesis of complex macromolecular architectures with controlled topology, which comprise chemically different (functional) blocks of controlled length in well-defined positions. Block co- and terpolymers, molecular and colloidal polymer brushes, and star-like polymers present just a few typical examples. Furthermore, miktoarm stars, core-shell stars and molecular brushes, etc. exemplify structures where chemical and topological complexity are combined in one macromolecule. 

Other types of IPN s exist, of course. For example, Johnson and Labana (1972) recently synthesized a modified type of latex IPN as follows A crosslinked polymer network I prepared by emulsion polymerization served as a seed latex to linear polymer II. The resulting semi-IPN exhibited the usual core-shell morphology. After suitable coagulation and molding steps, polymer II was selectively crosslinked to form a macroscopic network, resulting in a thermoset material. The topology of this IPN therefore involves microscopic network islands of polymer I embedded in a continuous network of polymer II. 

Summary Organosilicon p-networks are utilized as nanoreactors consisting of single crosslinked molecules. Functionalized core-shell particles with a core comprising reactive Si-H moieties are utilized to reduce noble metal salts like HAuCU to elemental gold clusters, which are topologically immobilized in the core of the networks. The preparation of hollow micro-networks leads to molecular containers which can be loaded with reactants. 

The active micro-reactors described above cannot be recycled because the SiH moieties cannot be renewed. Recyelable micro-networks may be realized in the form of passive miero-reactors which do not actively take part in the reaction but merely provide the confined reaction space. For this purpose hollow micro-networks are synthesized first, a micro-emulsion of linear poly(dimethyl-siloxane) (PDMS) of low molar mass (M = 2000-3000 g/mol) is prepared and the endgroups are deactivated by reaction with methoxytrimethylsilane. Subsequent addition of trimethoxymethyl-silane leads to core-shell particles with the core formed by linear PDMS surrounded by a crosslinked network shell. Due to the extremely small mesh size of the outer network shell the PDMS ehains become topologically trapped and do not diffuse out of the micro-network over periods of several months (Fig. 3). However, if the mesh size of the outer shell is increased by condensation of trimethoxymethylsilane and dimethoxydimethylsilane the linear PDMS chains readily diffuse out of the network core and are removed by ultrafiltration. The remaining empty or hollow micro-network collapses upon drying (Fig. 4). So far, shape-persistent, hollow particles are prepared of approximately 20 nm radius, which may be viewed as structures similar to crosslinked vesicles. At this stage the reactants cannot be concentrated within the micro-network in respect to the continuous phase. 

Hiickstadt, H., Goldacker, T, Gdpfert, A., and Abetz, V. (20(X)a) Core-shell double gyroid morphologies in ABC triblock copolymers with different chain topologies. Macromolecules, 33,3757-3761. 

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