In this contribution, we reported a facile synthesis of poly(methyl methacrylate)-block-poly(N-vinyl pyrrolidone) (PMMA-b-PVPy) diblock copolymers via sequential radical polymerizations mediated by isopropylxanthic disulfide (DIP). It was found that the radical polymerization of N-vinyl pyrrolidone (NVP) mediated by DIP was in a controlled and living manner. In contrast, the polymerization of methyl methacrylate mediated by DIP displayed the behavior of telomerization, affording xanthate-terminated PMMA with a good control of molecular weights while the conversion of monomer was not very high. The xanthate-terminated PMMA can be successfully used as the macromolecular chain transfer agent for the polymerization of NVP via RAFT/MADIX process and thus PMMA-b-PVPy diblock copolymers can be successfully synthesized via sequential radical polymerization mediated by isopropylxanthic disulfide. One of these diblock copolymers was incorporated into polybenzoxazine and the nanostructured thermosets were obtained as evidenced by transmission electron microscopy, small angle X-ray scattering, and dynamic mechanical thermal analysis. The formation of nanostructures in polybenzoxazine thermosets was ascribed to a reaction-induced microphase separation mechanism. (c) 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 952-962