Stabilization of Metal Nanoparticles in Aqueous Medium by Polyethyleneoxide-Polyethyleneimine Block Copolymers

The branched polyethyleneoxide-polyethyleneimine (PEO)n-b-PEI block copolymers are synthesized and fractionated. The (PEO)n-b-PEI block copolymers are found to be able to form micelles in aqueous solution after addition of certain metal compounds (H2PtCl6, Na2PtCl4, RhCl3). The degree of copolymer polydispersity seems to play an important role in metal nanoparticle stabilization. Comparison of diblock and branched copolymers shows that as a rule branched block copolymers are the better stabilizing systems for metal nanoparticles. In the case of micelle formation due to interaction with metal compounds, fine control on colloid morphology can be provided, which leads to very uniform particles. Variation of different parameters (such as concentration, pH, type of reducing agent) affects the nanoparticle morphology as well. Copyright 1999 Academic Press.