PNIPAM-based copolymer microgels as nanoreactors for the in situ synthesis of gold nanoparticles

Abstract

The combination of microgels and inorganic nanoparticles leads to hybrid systems with unique properties that are interesting for catalysis, optics, and biomedicine. A common strategy to incorporate nanoparticles into microgels is through encapsulation via seeded precipitation polymerization, leading to structurally well-defined core-shell microgels. An alternative and highly promising approach is the in situ nanoparticle formation within microgels. While this often leads to a random distribution of many nanoparticles per microgel, a challenge lies in the design of microgels that provide spatial control over nanoparticle formation to enable the formation of single nanoparticles in the central region of the microgels. In this study, we systemically investigate poly-N-isopropylacrylamide-based copolymer microgels as versatile nanoreactors for the in situ synthesis of gold nanoparticles. By incorporating the comonomers acetoacetoxyethyl methacrylate (AAEM) and acrylic acid (AAc), we shine light on the role of different functionalities for the in situ reduction and microgel colloidal stability. Importantly, depending on microgel composition and gold ion concentration, it is possible to synthesize single, monodisperse nanoparticles within each microgel. Additionally, we demonstrate that the formed nanoparticles can be overgrown through an easy one-step protocol. Our new hybrid copolymer microgels are colloidally stable and show pronounced deswelling/swelling behavior in response to temperature.