The high differential reactivity of methylmethacrylate (MMA) and vinylpyrrolidone (VP) in standard radical copolymerization allows the one-pot preparation of stable methylmethacrylate (MMA)-based solid particles by a surfactant-free process. The copolymers obtained in methanol exhibit a high compositional heterogeneity and a phase separation at high conversion. Partitioning of copolymer chains between the phases as a function of their composition has been observed, being the dispersed phase rich in copolymers with high content of hydrophobic MMA monomer and the continuous phase rich in copolymers with high content of hydrophilic VP monomer. The addition of water under stirring leads to formation of solid particles. The particles have shown a hierarchical structure composed of micron-size particles decorated with nano-size structures on their surface. The size of the nanostructures depends on the initial MMA/VP feed molar ratio in the copolymerization. (C) 2011 Elsevier Ltd. All rights reserved.