Spherical polyelectrolyte brushes consisting of a magnetite/polystyrene nanocomposite core and a poly(acrylic acid) brush shell were prepared by photo‐emulsion polymerization. They are narrowly dispersed, superparamagnetic and redispersible after aggregating by external magnetic field, as determined by transmission electron microscopy, dynamic light scattering, thermal gravimetric analysis and a vibrating sample magnetometer. Magnetic control is thus introduced into nano‐sized spherical polyelectrolyte brushes to achieve recovery and controllable delivery in applications. This approach opens up the way for cost‐effective applications of spherical polyelectrolyte brushes.
