Poly(methyl methacrylate)poly(acrylonitrile-co-butadiene) (PMMA-NBR) coreshell structured nanoparticles were prepared using a two-stage semibatch microemulsion polymerization system with PMMA and NBR as the core and shell, respectively. The Gemini surfactant 12-3-12 was used as the emulsifier and found to impose a pronounced influence on the formation of coreshell nanoparticles. The spherical morphology of coreshell nanoparticles was observed. It was found that there exists an optimal MMA addition amount, which can result in the minimized size of PMMA-NBR coreshell nanoparticles. The formation mechanism of the coreshell structure and the interaction between the core and shell domains was illustrated. The PMMA-NBR nanosize latex can be used as the substrate for the following direct latex hydrogenation catalyzed by Wilkinson's catalyst to prepare the PMMA-HNBR (hydrogenated NBR) coreshell nanoparticles. The hydrogenation rate is rapid. In the absence of any organic solvent, the PMMA-HNBR nanoparticles with a size of 30.6 nm were obtained within 3 h using 0.9 wt % Wilkinson's catalyst at 130 degrees C under 1000 psi of H(2). This study provides a new perspective in the chemical modification of NBR and shows promise in the realization of a "green" process for the commercial hydrogenation of unsaturated elastomers. (c) 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 50: 736-749, 2012