Self-assembled PHEA-based block copolymers for the synthesis of gold nanoparticles

Abstract

In this work, cholesteryl chloroformate (Chol) and cholic acid (CA) were conjugated into six-arm star-shaped poly(2-hydroxyethyl acrylate) (PHEA) polymers. These molecules were randomly attached to the hydroxyl groups of PHEA. The first block of PHEA contains around 2% of cholesterol and 13% of cholic acid. The resulting star (PHEA-co-PChol-co-PCA)₆ copolymers were then extended by further addition of HEA to form a second block. The copolymers self-assembled in an aqueous solution (D_H between 10–14 nm, by DLS). Next, these small aggregates were used to prepare in situ AuNPs without an additional reducing agent. The metallic nanoparticles were obtained in solution for four to six hours at 70 °C. The formation of AuNPs was only observed when the second block was long enough, between 120 to 180 repetitive units of HEA per arm. FE-SEM images show spherical nanoparticles, triangles, and pentagonal/hexagonal shapes. Only spherical nanoparticles were obtained by increasing the polymer concentration. The gold nanoparticles were obtained and kept stable from a polymer concentration of 0.5 g L⁻¹. Interestingly, with the increase in polymer concentration, the intensity of the absorption band of the AuNPs decreases noticeably. Furthermore, the reducing capacity of PHEA homopolymers was demonstrated in obtaining AuNPs. The development of nanosystems with small size and improved stability makes them promising for future research.