'Nano-tree'-type spherical polymer brush particles as templates for metallic nanoparticles

We present a new type of spherical polymer brush particles that consist of a solid poly(styrene) core (diameter: ca. 100 nm) onto which chains of a bottlebrush polymer have been densely grafted. These systems were prepared in aqueous dispersion by photo emulsion-polymerization using the macromonomer poly(ethylene glycol) methacrylate (PEGMA). In opposite to conventional spherical polyelectrolyte brushes carrying linear polymer chains, the system prepared here has a shell consisting of regularly branched chains ('nano-tree'-type morphology). The branches consist of oligo(ethylene glycol) chains (n=13) terminated by a hydroxyl group. We demonstrate that these particles can be used as nanoreactors for the generation and immobilization of well-defined silver nanoparticles. Cryo-TEM and FESEM images show that Ag nanoparticles with diameter of ∼7.5±2 nm are homogeneously embedded into the PS-PEGMA brushes. Moreover, the composite particles exhibit an excellent colloidal stability. The catalytic activity is investigated by monitoring the reduction of 4-nitrophenol by NaBH4 in presence of these silver nano-composite particles. The rate constant kapp was found to be strictly proportional to the total surface of the nanoparticles in the system. The study of the temperature dependence shows that the rate constants kapp obtained at different temperatures leads to an activation energy of 62 kJ/mol.