The effect of polymer branching and average molar mass on the formation, stabilization and thermoresponsive properties of gold nanohybrids stabilized by poly(N-isopropylacrylamides)

Abstract

Branched structures are of crucial importance in the formation of hybrid materials with tunable properties. Nevertheless, little is known about the optimal macromolecular parameters (molecular weight, extent of branching etc.) allowing either control of the growth mechanism of the inorganic core or access to nanohybrids with high colloidal stability. In this paper, the synthesis and characterization of a new family of dendritic polymers comprising a branched polyamidoamine core and a poly(N-isopropylacrylamide) shell are described. In aqueous solutions, a strong dependence of their thermoresponsiveness upon the macromolecular architecture was evidenced by neutron and light scattering techniques and electronic microscopy. These polymers were then employed as stabilizers of gold nanoparticle (AuNP) dispersions by either a posteriori adsorption on NPs or in situ NP formation. Both approaches were successful for stabilization and reversibility of the thermostimulable precipitation process. First, we demonstrated that macromolecular architecture greatly influences the growth mechanism of the in situ formed NPs and their colloidal stability. Whereas small linear polymers allow a better control of NP growth, the branched structures proved to be better stabilizing agents. In contrast, adsorption on preformed AuNPs of controlled size evidenced the higher efficiency of small branched structures than linear or hyperbranched polymers as good stabilizing agents.