Self-Assembled Diblock Copolymer "Nanoreactors" as "Catalysts" for Metal Nanoparticle Synthesis

The self-assembly and selective distribution of metal or metal oxide nanoparticles in block copolymer matrices was designed to produce photonic bandgap materials through a bottom-up method rather than the more common top-down approach. The synthesis of such materials consists of the in situ thermolysis of metal carbonyl precursors in a diblock copolymer solution. Reaction rates of the formation of nanoparticles in solution were measured to better understand and control the course and final products of the reactions. Our results showed that the rates for reactions performed in a diblock copolymer solution are much faster than the rates of the same reactions performed in a homopolymer solution. The reaction rates for the thermolysis of three different metal carbonyl precursors, Cr(CO)(6), Fe(CO)(5), and CO2(CO)(8), show that this phenomenon is not specific to the type of metal carbonyl precursor, but rather, to the type of polymer in solution. Polystyrene (PS) and poly(methyl methacrylate) (PMMA) were used as a model system both as homopolymers and as diblock copolymers. Our results showed that the arrangement of the diblock copolymers in solution into spherical internal-external (i.e., core-shell) domains created self-assembled "nanoreactors" with PS acting as the surrounding shell while the internal PMMA domain (core) contained high precursor concentration, resulting in faster kinetics. Furthermore, we have found that the arrangement of the diblock copolymer into these ordered structures in solution does not occur spontaneously, but is rather facilitated by a synergistic coupling effect with the metal carbonyl precursor.