Synthesis of metallic nanoparticles within pH-sensitive polymeric matrices

Abstract

Two different classes of pH-responsive polymeric nanostructures have been utilised as nanoreactors for the growth of colloidal metal particles. The first class consists of the micellar cores of double hydrophilic block copolymers, whereas in the second case pH-sensitive microgels are used. The micelles are formed by PHEGMA-b-PDEAEMA diblock copolymers synthesised by group transfer polymerisation. The hydrophobic PDEAEMA block is pH-responsive: at low pH it can be protonated and it becomes hydrophilic, leading to molecular solubility, whereas at higher pH micelles are formed with the hydrophobic PDEAEMA blocks immobilised within the micellar cores; the behaviour is investigated by potentiometric titration, DLS, 1H-NMR and AFM. Lightly cross-linked latex particles based on DEAEMA monomer are synthesised by emulsion polymerisation. These particles exhibit reversible swelling properties in water studied by DLS. At low pH they exist as swollen microgels due to protonation of the tertiary amine units whereas deswelling occurs above pH 7 leading to the formation of the original latexes. Metal nanoparticles were synthesised within both the micellar cores and the microgels by the incorporation of H 2PtCl 6 and subsequent reduction using NaBH4. Micelle transformations upon metallation were studied using DLS. The polymer-metal interactions were investigated by UV-Vis spectroscopy whereas the nanoparticles were investigated by TEM and XRD.