The synthesis of polymeric nanocapsules by means of miniemulsion cationic polymerization has been investigated here. The core-shell structure was obtained by confining the reaction at the interface between continuous and dispersed phase of an oil-in-water miniemulsion. This hallmark also allows to carry out the cationic UV-activated polymerization of a vinyl monomer, namely triethylene glycol divinyl ether, in water. The study firstly focused on formulation design. Various kinds of surfactant were examined and SDS provided optimal miniemulsion stability. Moreover, several amounts of surfactant, photoinitiator and oil were tested to optimize formulation composition. Nanocapsules were successfully synthesized and their average size, dimensional distribution, surface zeta potential, stability over time, morphology and thermal behavior were explored. Then, processing conditions, namely irradiation time and sonication time, were investigated. Results highlighted the possibility to design nanocapsule dimension by acting on ultrasound exposure time and a minimum size of 200 nm was identified. (C) 2018 Elsevier Ltd. All rights reserved.