Plasma-initiated controlled/living radical polymerization of methyl methacrylate (MMA) was carried out in the presence of 2-cyanoprop-2-yl 1-dithionaphthalate. Well-defined poly(methyl methacrylate) (PMMA), with a narrow polydispersity, could be synthesized. The polymerization is proposed to occur via a RAFT mechanism. Chain-extension reactions were also successfully carried out to obtain higher molecular weight PMMA and PMMA-block-PSt copolymer.