Interaction of metal compounds with 'double-hydrophilic' block copolymers in aqueous medium and metal colloid formation

The interaction of a 'double-hydrophilic' polyethyleneoxide-polyethyleneimine block copolymer (PEO-b-PEI) with AuCl3, PdCl2, Na2PdCl4, H2PtCl6. 6H(2)O, Na2PtCl6. 6H(2)O, and K2PtCl4 in aqueous medium was studied. Micellar structure formation was observed for all metal compounds except Na2PdCl4 where additional protonation of the polymer was required to induce micelle formation. The characteristics of the micelles formed depended strongly on the metal type, the molar ratio polymer:metal compound, and the type of reducing agent. Micellization in the presence of AuCl3. H2O is accompanied with reduction of the salt and the formation of gold colloid without reducing agent induced by oxidation of the PEI block. The interaction with PtCl62- ions results in narrowly distributed micelles with size depending on the metal compound loading. In the case of loading with H2PtCl6, it was found that the size and shape of the colloids can be controlled by changing the molar ratio PEI:metal salt. The lower is the metal loading, the smaller are the particles. In addition, differently shaped Pt colloids were observed. This phenomenon can be controlled by the relative ratio of reactants. (C) 1998 Elsevier Science S.A. All rights reserved.