Preparation of Janus Hybrid Gold Nanoparticles Based on Asymmetric Star Polymers

A highly efficient and simple method for preparing small-size Janus gold nanoparticles (AuNPs) capable of self-assembling was developed. Firstly, the asymmetric star polymers ((LA)₇-CD-(PNIPAM₄₆)₁₄) were fabricated based on β-cyclodextrin (β-CD) by combining atom transfer radical polymerization (ATRP) and click chemistry. Secondary, the hydroxyl groups on the wide cross-section of the β-CD molecule were modified to be ATRP initiator moieties, which then initiated the polymerization of N-isopropyl acrylamide (NIPAM) to form fourteen PNIPAM chains via ATRP. The primary hydroxyl groups on the narrow cross-section of the β-CD molecule were converted into azide groups and then coupled with 5-(1,2-dithiolan-3-yl)-N-(prop-2-ynyl) pentanamide molecules by click chemistry. The obtained asymmetric star polymers ((LA)₇-CD-(PNIPAM₄₆)₁₄) were used to modify AuNPs that were formerly surface-stabilized by n-butylthiol through the ligand exchange process. Due to the steric effect of (LA)₇-CD-(PNIPAM₄₆)₁₄ macromolecules, Janus hybrid AuNPs, Au_3.1-CD-(PNIPAM₄₆)₁₄, with amphiphilic surface were prepared, which could self-assemble in water into micelle-like aggregates, i.e. supermicelles. The chemical and chain structures of asymmetric (LA)₇-CD-(PNIPAM₄₆)₁₄ star polymers and the amphiphilic Janus hybrid Au_3.1-CD-(PNIPAM₄₆)₁₄ nanoparticles were characterized by Nuclear Magnetic Resonance (NMR), Matrix-Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS), Gel Permeation Chromatography (GPC) and Thermal Gravimetric (TG) analysis. The morphology and structure of the prepared micelle-like self-assemblies were investigated by Transmission Electron Microscope (TEM).