Thermoresponsive Amphiphilic Diblock Copolymers Synthesized by MADIX/RAFT: Properties in Aqueous Solutions and Use for the Preparation and Stabilization of Gold Nanoparticles

Well-defined diblock copolymers comprising thermosensitive poly(N-isopropyl acrylamide) (PNIPAM) and poly(n-butylacrylate) (PBA) blocks were synthesized by macromolecular design by interchange of xanthates (MADIX)/reversible addition-fragmentation chain transfer polymerization (RAFT) using a xanthate-type mediating agent. Their behavior in aqueous solution as a function of temperature was studied by scattering and microscopy techniques. The cloud point temperature values were strongly correlated to the hydrophobic content of the copolymers. Moreover, above the cloud point, the block copolymer structure led to the formation of large reversible aggregates with well-defined sizes. Those polymers were then used to study the synthesis and stability of gold nanoparticles (AuNPs) dispersions either by coating preformed AuNPs or by in situ preparation. In this latter case, we showed that the appropriate choice of polymer concentration allows one to control the size of the AuNPs. Furthermore, the AuNPs were embedded within globules of diblock copolymers, this type of architecture providing long-term stability as well as a thermosensitivity to the AuNPs.