Preparation of Polymer Brush Grafted Anionic or Cationic Silica Nanoparticles: Systematic Variation of the Polymer Shell

Polymer brush grafted anionic SiO₂@PMAA (poly­(methacrylic acid)) and cationic SiO₂@PDMAEMA (poly­(2-(dimethyl­amino)­ethyl methacrylate)) inorganic/polymer hybrid nanoparticles with different core radii (d_NP = 50–140 nm) and different amounts of attached polymer were synthesized via surface-initiated atomic transfer radical polymerization (ATRP). To avoid irreversible aggregation, a three-step surface modification had to be employed, thereby keeping the nanoparticles always dispersed. For SiO₂@PMAA the shell thickness changes with the monomer concentration, while for SiO₂@PDMAEMA the grafting density was changed by monomer concentration and the shell thickness remained constant. We assume that the control over the grafting density relies on the nature of the complexation potential of the PDMAEMA. The structural characterization of the polymer grafted SiO₂-NPs was done in detail by different scattering methods combined with thermogravimetric analysis, and details of the brush characteristics are obtained by small-angle neutron scattering (SANS). With this approach we were able to produce silica nanoparticles with anionic and cationic polymer shells, where the softness of the NPs can be controlled by the amount of polymer, which are pH-responsive and colloidally stable over a large pH range.