Hybrid single-chain nanoparticles via the metal induced crosslinking of N-donor functionalized polymer chains

Single-chain nanoparticles (SCNPs) formed via the crosslinking of isolated polymer chains in highly diluted solutions represent a conveniently achievable class of well-defined small particles. Due to their partly swollen geometry, they provide huge surface areas along the polymer chain. Herein, we present a set of copolymers based on poly(n-butyl acrylate-co-4-vinylpyridine) with molecular weights ranging from 6000 to 70 000 g mol−1 and an amount of metal binding sites ranging from 3 to 22 mol%. These organosoluble precursors with hydrophobic side chains were treated with Cu2+, Co2+, Ni2+, Zn2+, Fe2+, Mg2+, and Pd2+. The coordination of metal ions to pyridine moieties as versatile N-donors leads to intrachain crosslinking and subsequent chain collapse. Overall, a set of 34 hybrid SCNPs was prepared. SCNP formation was monitored by dynamic light scattering and diffusion ordered NMR spectroscopy. The influence of the molecular weight, the molecular weight distribution, and the amount of binding sites on size reduction during SCNP formation is discussed in the context of models given in the literature. Additionally, an indication for the dependency of size reduction on the coordinative bond strength is given. Selected crosslinking metal centres have been analyzed by theoretical investigations. A significant freedom for the coordination geometry which can induce chain collapse is revealed.