Preparation of Polymer-Protected Colloidal Dispersions of Copper

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Abstract
Colloidal copper dispersions are prepared by reducing copper(II) ions in water with sodium tetrahydroborate or hydrazine in the presence of various protective polymers. The polymers are poly(N-vinyl-2-pyrrolidone), poly(vinyl alcohol), poly(methyl vinyl ether), poly(potassium vinyl sulfate), dextrin, amylopectin, methylamylopectin, methylcellulose, ethylcellulose, and (2-hydroxyethyl)cellulose. The dispersions are black, reddish dark brown, or reddish brown homogeneous solutions, and are stable under nitrogen at room temperature for more than three months. Electron diffraction experiments indicate that copper atoms in the colloidal particles are arranged in an ordered way, which is almost identical with that in a crystal of bulk copper metal. At the charged molar ratio 40 of the monomeric residue of the protective polymer to copper(II) ion, the average diameters of the copper particles, prepared by use of sodium tetrahydroborate, range from 50 to 150 Å, depending on the polymer used. With the use of poly(N-vinyl-2-pyrrolidone) as protective polymer, the size of the copper particles monotonously increases with increase in the degree of polymerization of the polymer and also with decrease in the amount of the polymer.

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