Stabilization of metal nanoparticles in aqueous medium by polyethyleneoxide-polyethyleneimine block copolymers

The branched polyethyleneoxide-polyethyleneimine (PEO)(n)-b-PEI block copol ymers are synthesized and fractionated. The (PEO)(n)-b-PEI block copolymers are found to be able to form micelles in aqueous solution after addition o f certain metal compounds (H2PtCl6, Na2PtCl4, RhCl3). The degree of copolym er polydispersity seems to play an important role in metal nanoparticle sta bilization. Comparison of diblock and branched copolymers shows that as a r ule branched block copolymers are the better stabilizing systems for metal nanoparticles. In the case of micelle formation due to interaction with met al compounds, fine control on colloid morphology can be provided, which lea ds to very uniform particles, Variation of different parameters (such as co ncentration, pH, type of reducing agent) affects the nanoparticle morpholog y as well. (C) 1999 Academic Press.