A novel photoreactor to facilitate electrosteric stabilization of colloidal polymer particles is presented. Anionic and cationic polystyrene particles having a diameter of ca. 100 nm and bearing a thin layer of photoinitiator are used as seed colloids. Anionic and cationic chains of weak or strong polyelectrolytes are grafted onto the surface of these particles. The polyelectrolyte chains are densely tethered onto the surface of the polymer particles. For this purpose, a commercial photoreactor setup developed for water and liquid waste treatment has been adapted. Compared to the photoreactor used earlier for photoemulsion polymerization, the new reactor largely shortens the reaction times and improves the reproducibility of the reaction. This is achieved by the higher UV power and controlled radiation times and power. (C) 2008 Elsevier B.V. All rights reserved.