A Versatile Route to Shape Polymer Nanoparticles by Deforming Nanoreactors Made from Magnetic Surfactants

Abstract Directions are equivalent in an amorphous system, so anisotropy cannot emerge of its own accord, resulting in a gap for preparing polymer nanoparticles deviating from a spherical shape. Unlike inorganic nanocrystals for which faceting controls shape, polymers are not directly available as rod‐like particles, for instance. Here, we show a highly versatile, nontoxic, novel approach to break this paradigm and obtain polymer nanorods by emulsion polymerization using a unique surfactant comprising a magnetic head group. Surprisingly, even applying a weak magnetic field to the magnetic surfactant within an emulsion polymerization transforms diamagnetic polymers into rod‐like nanoparticles instead of their usual spherical shapes. The polarization in a magnetic field exerts a torque on the molecular structure, and as a result, the emulsion droplets deform. The method can be applied to different polymers such as polystyrene, polymethylmethacrylate, or polythiophene. The magnetic surfactant is recovered quantitatively and can be reused; one obtains metal‐free polymer particles, and the process is sustainable. The straightforward approach presented here will unlock several applications of these previously inaccessible polymer nanorods, particularly in the case of conducting polymers.