Hyperbranched poly(ethylenimine) (PEI) with amino groups or carbohydrate terminal groups have been used as support materials for metal nanoparticles (i.e., Cu, Ag, Au, and Pt) in water. Various parameters have been optimized, such as pH, concentration of the polymer in solution, and [metal ions]/[polymer] ratio in order to obtain stable metal nanoparticles with a narrow size distribution. TEM measurements revealed that particles with a diameter as low as 1.4 nm were obtained. An increase of stability was obtained after functionalization of PEI with glycidol, gluconolactone, or lactobionic acid. In the case of Pt the catalytical activity of the corresponding nanoparticles was evidenced.

Successful one-pot preparation of a hyperbranched polymer chemically analogous to PAMAM dendrimers was achieved and its use for metal nanocluster stabilization is reported. When compared to PAMAM, such experiments demonstrate clearly the effect of the macromolecular architecture on the formation of the inorganic nanoparticles.Small metal particles have quite unique optical, electronic, and catalytic properties that result from size, shape, and size distribution effects.The preparation of such metal colloids requires the use of stabilizers which prevent the thermodynamically favored aggregation of the nanoparticles in solution. Various well-known compounds (e.g., water-soluble polymers, surfactants, etc.) have been employed as stabilizers. 1 Dendrimers have also been used as nanoreactors in which metal cations are localized before reduction leading to stabilized metal nanoparticles of a few nanometers, 2 this small size being presumably related to the unique structure of the dendrimers. However, the costly synthesis of dendrimers is prohibitive for many applications. In contrast to those perfectly branched monodisperse dendrimers, randomly branched (i.e., hyperbranched) polymers can be easily accessible 3 and they can effectively stabilize metal nanoparticles in organic solvents. 4 To our knowledge, no attempt has been made, up to now, to compare nanoparticles obtained from reduction of metal salts complexed with dendrimer and hyperbranched polymer.In this work, we present the synthesis and characterization of a hyperbranched polymer that is chemically analogous and close in molecular weight to the 4th generation of PAMAM dendrimers (noted PAMAM4). Because of this similarity in the molecular weights, this hyperbranched polymer was noted HYPAM4. Characterization of gold nanoparticles prepared using these polymers is also described.Polymer Synthesis 5 and Characterization. The synthesis of hyperbranched polyamidoamines with a structure similar to the one of PAMAM dendrimers was based on a method described by Dvornic, 6 where a hexaester was reacted with a triamine (Figure 1). This method has the strong advantage of leading to hyperbranched architectures in a single step and can be carried out in large quantities. By adjusting the mole ratio between the hexaester and the triamine for the polymer synthesis, control of the final molar mass of the hyperbranched polymer can be experimentally achieved. We have focused our work on the samples obtained when a triamine/hexaester mixture of 10:1 ratio was used for the synthesis. Clearly, the characterization of this polymer demonstrates that HYPAM4 is quite comparable to the highly used PAMAM dendrimer of the 4th generation. Molar masses are very close for both compounds, as are the numbers of primary and tertiary amines (see Table 1) (by construction, HYPAM4 has, however, less amide functions when compared to PAMAM4). Indeed, to check the chemistry of the hyperbranched polymer, the quantification of amine groups was carried out by several methods. The most reliable results ...