Block copolymer micelles nanoparticles

Colloidal catalysts in alkyne hydrogenation are widely used in conventional solvents, but their reactivity and high efficiency were very attractive for application in scC02. This method, which is based on colloidal catalyst dispersed in scC02, yields products of high purity at very high reactions rates. Bimetallic Pd/Au nanoparticles (Pd exclusively at the surface, while Au forms the cores) embedded in block copolymer micelles of polystyrene-block-poly-4-vinylpyridine... 

In a more general way, the loading of metal salts into preformed block copolymer micelles has become the most used route for the incorporation of precursors into block copolymer nanostructures because it allows precursor loading with tolerable loading times, it is quite versatile, and it is applicable to a wide variety of precursor/block copolymer/solvent systems. The accordingly synthesized polymer-coated metallic or semiconducting nanoparticles exhibit increased stability, which results in, e.g., protection against oxidation as illustrated by Antonietti et al. [108]. 

T. F. Jaramillo, S. H. Baeck, B. R. Cuenya, and E. W. McFarland, Catalytic activity of supported au nanoparticles deposited from block copolymer micelles, J. Am. Chem. Soc. 125, 7148-7149... 

Application of amphiphilic block copolymers for nanoparticle formation has been developed by several research groups. R. Schrock et al. prepared nanoparticles in segregated block copolymers in the sohd state [39] A. Eisenberg et al. used ionomer block copolymers and prepared semiconductor particles (PdS, CdS) [40] M. Moller et al. studied gold colloidals in thin films of block copolymers [41]. M. Antonietti et al. studied noble metal nanoparticle stabilized in block copolymer micelles for the purpose of catalysis [36]. Initial studies were focused on the use of poly(styrene)-folock-poly(4-vinylpyridine) (PS-b-P4VP) copolymers prepared by anionic polymerization and its application for noble metal colloid formation and stabilization in solvents such as toluene, THF or cyclohexane (Fig. 6.4) [42]. 

JaramUlo TF, Baeck S-El, Cuenya BR, McFarland EW (2003) Catalytic Activity of Supported Au Nanoparticles Deposited from Block Copolymer Micelles. J Am Chem Soc 125 7148-7149... 

Block copolymers self-assemble to form nanoscale organized structures in a selective solvent. The most common structures are spheres, with the insoluble core surrounded by a solvent-swollen corona. In some instances, disk- or worm-like micelles form, and are of particular interest, since the control of their association can lead to a broad range of new applications [1,2]. An important subset of block copolymer micelles are those which contain metal atoms, through covalent attachment or by complexa-tion [3], These structures are interesting because they take advantage of the intrinsic properties of their components, such as the mechanical properties of the polymer micelles and the optical and magnetic characteristics of the metal atoms. Moreover, the assembly permits the control of the uniformity in size and shape of the nanoparticles, and it stabilizes them. 

Nanoparticles consisting of noble metals have recently attracted much attention because such particles exhibit properties differing strongly from the properties of the bulk metal [1,2], Thus, such nanoparticles are interesting for their application as catalysts [3-5], sensors [6, 7], and in electronics. However, the metallic nanoparticles must be stabilized in solution to prevent aggregation. In principle, suitable carrier systems, such as microgels [8-11], dendrimers [12, 13], block copolymer micelles [14], and latex particles [15, 16], may be used as a nanoreactors in which the metal nanoparticles can be immobilized and used for the purpose at hand. 

Selvan and coworkers167168 utilized a block copolymer micelle of polystyrene-block-poly(2-vinylpyridine) in toluene exposed to tetrachloroauric acid that was selectively adsorbed by the micelle structure. On exposure of this solution to pyrrole monomer, doped PPy was obtained concurrently with the formation of metallic gold nanoparticles. The product formed consisted of a monodispersed (7-9 nm) gold core surrounded by a PPy shell. Dendritic nanoaggregate structures were also reported... 

An example of a consecutive use of block copolymer micelles as endo- and exo-templates is the preparation of mesoporous silica with embedded Pd-nanoparticles [113]. As a first step Pd-nanoparticles are prepared in the micellar core (see Sect. 4.1). In a lyotropic phase of these micelles they are further employed as exotemplates for the preparation of mesoporous silica (see Sect. 5). After removal of the block copolymer by calcination, nanoparticles within the open mesopore structure are obtained (Fig. 20). This represents a promising way to incorporate catalytically active nanoparticles into mesoporous oxides as stable catalyst supports. 

This approach was first described in [64, 65]. When metal nanoparticles are located in the block copolymer micelle cores [64] or in microgels [65] and these polymeric systems are used as templates for silica casting, both pore size and... 

Unlike regular block copolymer micelles which are well permeable for reagents, triblock nanospheres with hydroxylated polyisoprene coronas, cross-linked poly(2-cinnamoyloxyethyl methacrylate) shells, and poly(acrylic acid) cores, filled with Pd nanoparticles, showed slower hydrogenation of alkenes than Pd blacks due to the need for the reactant(s) to diffuse into and the products to diffuse out of the encapsulating nanospheres [13]. On the other hand, microspheres formed by diblock poly(t-butyl acrylate)-hlocfe-poly(2-cinnamoyloxyethyl methacrylate) and filled with Pd nanoparticles demonstrated good permeability and higher catalytic activity in the hydrogenation of methyl methacrylate than the commercial Pd black catalyst [14]. 

In 1997, Antonietti et al. reported on catalytically active palladium nanoparticles prepared by reduction of palladium(II) compounds in inverse block copolymer micelles, namely polystyrene-ib-poly(4-vinylpyridine) (PS-b-P4VP). Activated aryl bromides were coupled reproducibly in Heck reactions [18]. Small partide sizes were a prerequisite for high conversions, as indicated by qualitative TEM investigations. Very high total turnovers were reported (0.0012 mol% palladium, 68% conversion in five days, corresponding to 56 000 TO) (Table 1). Catalyst activity was found to be dependent on the structure of the block copolymer employed, which was attributed to a better accessibility of the metal particles in smaller micelles with a high surfacer area and thinner polystyrene layer. 

Recently, block copolymers micelles filled with MoS nanoparticles (well miscible with mineral oil) were synthesized in heptane using interaction of Mo(CO)e with polystyrene-fc/ock-polybutadiene (PS-fc-PB) and polystyrene-i /ock-polyisobutylene (PS-fc-PIB) followed by H2S treatment [39]. To position MoS c nanoparticles in the PS core, the reaction between Mo(CO)e and block copolymer should be carried out in argon atmosphere. This yields arene Mo tricarbonyl complexes while olefin Mo carbonyl complexes do not form. By contrast, to place MoS nanoparticles in the PB corona, complexation with Mo(CO)e should be carried out in the CO atmosphere. This suppresses forma-... 

Unlike PEO- -P2VP, the PEO-fe-PB block copolymer micelles in water are very dense, so they successfully fulfill two roles They serve as nanoreactors for Pd, Pt, and Rh nanoparlicle formation and as metal-particle-containing templates for mesoporous silica casting [41]. Figure 4.10 presents PEO- -PB micelles (M = 13,400 = 19,200) filled with Pd nanoparticles and meso-... 

This chapter illustrates our approaches in the design of metal nanocomposites, both in bulk and in solution. The key advantages of soluble systems, especially if they retain solubility alter nanoparticle formation, are their potential use for raicroheterogeneous catalysis and magnetic liquids or formation of thin deposited or free-standing films (the latter were obtained with block copolymer micelles and some functional polysilsesquioxane colloids). These opportunities... 

TYR Tyrrell, Z., Winoto, W., Shen, Y., and Radosz, M., Block copolymer micelles formed in supercritical fluid can become water-dispensable nanoparticles Polytethylene glycol)-Z)/ocA -poly(8-caprolactone) in trifluoromethane, Ind. Eng. Chem. Res., 48, 1928, 2009. 

Yan B, Boyer J-C, Branda NR, Zhao Y (2011) Near-infrared light-triggered dissociation of block copolymer micelles using upconvertmg nanoparticles. J Am Chem Soc 133 19714... 

Notably, gold is by no means the only material that can be incorporated into block copolymer micelles. Indeed, other metals such as palladium, silver, and cobalt have been successfully applied, and even nanoparticles of CdS and PbS have been... 

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