Amphipolar core-shell cylindrical brushes as templates for the formation of gold clusters and nanowires

Methacryloyl end-functionalized block copolymers consisting of styrene and vinyl-2-pyridine were polymerized to poly(block co-macromonomer)s with a much higher main chain than side chain degree of polymerization. Like homo-polymacromonomers these molecules exhibit the structure of cylindrical brushes. Since the vinylpyridine block is coupled to the polymerizable group, the resulting cylindrical macromolecules exhibit a core of vinylpyridine and a shell of polystyrene, thus forming an amphipolar core-shell cylindrical macromolecule. The core-shell character of the molecules was demonstrated by HRTEM utilizing selective positive staining for the core and for the core and the shell. The core of the cylindrical brushes was loaded with HAuCl4 in toluene or methylene chloride followed by reduction of the noble metal salt by the electron beam, by UV light, or by chemical reducing agents. Depending on the amount of complexed noble metal ions and the reduction conditions, either a linear array of noble metal cluster or a continuous nanowire is formed most probably within the core of the cylindrical brushes. The resulting metal nanowires are much longer than the individual core-shell macromolecules which is caused by a yet unexplained specific end-to-end aggregation of the cylindrical polymers upon loading with HAuCl4.