Dendrimers are a new class of three-dimensional, man-made molecules produced by an unusual synthetic route which incorporates repetitive branching sequences to create a unique novel architecture. Exceptional features of the dendritic architecture include a high degree of structural symmetry, a density gradient displaying an intra-molecular minimum value and a well defined number of terminal groups which may be chemically different from the interior. The combination of these features creates an environment within the dendrimer molecule which facilitates trapping of guest species. Recently, dendritic polymers have been used as soluble templates/unimolecular reactors from which nano-clusters of inorganic compounds or elements can be synthesized. The basic concept involves using dendrimers as hosts to preorganize small molecules or metal ions, followed by a simple in situ reaction which will immobilize and stabilize domains of atomic or molecular guest components (inorganic compounds as well as elemental metals). In one of these examples poly(amidoamine) (PAMAM) dendrimers have been used, to attract copper(II) ions inside the macromolecules where they are subsequently reacted with solubilized H 2S to form metal sulfides. These organic/inorganic, dendrimer-based hybrid species have been termed 'nanocomposites’ and display unusual properties. For example, solubility of the nanocomposites is determined by the properties of the host dendrimer molecules. This allows for solubilization of the inorganic guest compounds in environments in which they are inherently insoluble. Since it has been established that there is no covalent bond between host and guest, these observations suggest that the inorganics are physically and spatially restricted by the dendrimer shell. However, this structure has not been verified. In this investigation a preliminary understanding of the physical structure of these dendrimer-based nanocomposites was sought. A model system of PAMAM dendrimer–copper sulfide nanocomposites was studied in various stages of its formation using a combination of small angle X-ray and neutron scattering experiments. The results suggest that little perturbation of the dendritic species occurs on complexation, but indicate that a secondary super-molecular aggregation phenomena occurs within nanocomposite solutions.
Посилання на статтю:
A small angle scattering study of dendrimer–copper sulfide nanocomposites / N.C. Beck Tan, L. Balogh, S.F. Trevino, D.A. Tomalia, J.S. Lin // Polymer. – 1999. – N 40. – P. 2537–2545.