The aqueous photo-living radical polymerization of sodium methacrylate (NaMA) was attained using 2,2′-azobis { 2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]-propionamide } (V-80) as the initiator and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (HTEMPO) as the mediator in the presence of (4-fluorophenyl)diphenylsulfonium triflate (FS). The polymerization was carried out in water at room temperature by irradiation using a high-pressure mercury lamp. Whereas the polymerization by V-80 and/or FS in the absence of HTEMPO produced polymers with very high molecular weights and broad molecular weight distributions, the HTEMPO-mediated polymerization provided still lower-molecular-weight distributions using both V-80 and FS. The first-order time-conversion plots had an induction period up to 2.5？h; however, they thereafter showed a linear increase. The conversion-molecular weight plots also exhibited a linear correlation. A linear correlation was also obtained for the plots of the molecular weights versus the reciprocal of the initiator concentration. Based on these three correlations, it was found that the HTEMPO-mediated photopolymerization proceeded by a living mechanism. 1. Introduction Poly(sodium methacrylate) (PNaMA), a water-soluble polyelectrolyte, has been used for many objectives, such as surface modification of the wettability and friction [1], suppression of cell adhesion and protein adsorption [1, 2], and self-assembly studies on amphiphilic block copolymers in aqueous media [3–7]. While PNaMA and its copolymers were prepared through the living anionic or living radical polymerizations of methacrylates with protecting groups of tert-butyl and benzyl, followed by deprotection [3–7], those were also directly obtained by the controlled/living radical polymerization of sodium methacrylate (NaMA) in water. For instance, the atom transfer radical polymerization (ATRP) of NaMA produced PNaMA with a well-controlled molecular weight [8]. This aqueous ATRP was used for the preparation of polymer brushes including PNaMA segments on gold [9, 10] and glass [11] surfaces. The photo-iniferter polymerization using a dithiocarbamate catalyst also succeeded in fabricating a PNaMA-branched graft copolymer on glass [12] and a poly(ethylene terephthalate) film [1]. In recent years, the nitroxide-mediated photo-controlled/living radical polymerization has been established for methyl methacrylate (MMA) using the derivatives of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) in the presence of the photo-acid generator (PAG) of diaryliodonium hexafluorophosphate
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