Preparation and optical properties of colloidal Ag⁰ nanoclusters from reduction of solution ionomer Ag-carboxylate ionic aggregates activated by swelling of covalently attached chain segments

Small colloidal Ag⁰ nanoclusters successfully were prepared from solution reaction of CH₃COOAg with a copolymer acid, poly(methyl methacrylate-ran-methacrylic acid) (MMA–MAA), in a methanol-containing solvent at room temperature in the dark in the absence of a typical chemical reductant. Tentatively mechanistically, slow PMMA-ionomerisation of the Ag⁺ ions produces intramolecular –COO⁻–Ag⁺ aggregate cross-links in the solution, which, upon swelling of the chain segments covalently bound to them, are activated by the resultant elastic forces to dissociate instantaneously at the O–Ag coordination bonds to give bare (i.e. uncoordinated), highly oxidative Ag⁺ ions, which are subject to reduction by the active α-H atoms of the solvent methanol to make Ag⁰ nanoclusters supported by the re-formed MMA–MAA; the MMA–MAA acid-copolymer, without itself undergoing any permanent chemical change, serves as a mechanical-activator or, say, catalyst for the mechanochemical reduction of CH₃COOAg. This novel, facile approach may universally be extended to fabricate other transition-metal nanoclusters deposited in diverse polymeric matrices.