A synthetic methodology is described for the preparation of coreshell nanogels by reversible addition-fragmentation chain transfer. Well-defined macro chain transfer agents (macro-CTA's) were prepared in a first step using monomers that yield sensitive polymers. In the second step, a crosslinker alone or with the addition of a functionalized comonomer were used to form a crosslinked core. The ratio of crosslinker to macro-CTA is crucial to yield nanogels. Furthermore, the polymerization time has an impact in the architecture of the nanomaterial obtained: it evolves from a core-crosslinked star to a coreshell nanogel. Controlling the molecular weight of the macro-CTA and the type of comonomer in the core forming step, coreshell nanogels with hydrodynamic diameters from 22 to 168 nm and a core that represents from 35 to 77% of the size, were prepared containing functional groups in the core which could be used as catalytic scaffolds. (c) 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012.