Template-Directed Synthesis of Silica Nanowires and Nanotubes from Cylindrical Core-Shell Polymer Brushes

We report the synthesis and characterization of core-degradable core-shell cylindrical polymer brushes (CPBs) that can be used as a molecular soft template for the fabrication of uniform one-dimensional silica nanostructures with tunable dimensions and morphologies. The silica nanostructures were templated from CPBs consisting of a densely grafted poly(epsilon-caprolactone) core and a poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) shell. According to the degree of polymerization of both the backbone and the side chains, silica nanostructures with varying lengths and diameters were obtained. The weak polyelectrolyte shell acted as an ideal nanoreactor for the deposition of silica. Calcination or treatment with an acid of the as-synthesized silica hybrids led to the removal of the core and consequently to hollow silica nanotubes. Calcined nanotubes were microporous and exhibited high pore volumes and high specific surface areas. Furthermore, metal salts immobilized within the PDMAEMA shell can be fully embedded into the silica shell. Accessibility of the embedded nanoparticles was demonstrated via the catalysis of the reduction of 4-nitrophenol by sodium borohydride in the presence of nanoparticle-doped silica hybrids.