Photopolymerizations of N-isopropylacrylamide (NIPAAm) were carried out in water, initiated by 2-(N,N-diethyldithiocarbamyl)isobutyric acid sodium salt (DTCA-Na) as water-soluble initiator under UV irradiation. The first-order time-conversion plots showed slowly decreasing slopes indicating a slow decrease of the active radical concentration. The number-average molecular weight (M-n) of the obtained poly(N-isopropylacrylamide) (PNIPAAm) increased in direct proportion, roughly, to monomer conversion. Until ca. 60% of conversion, the polydispersity was relatively narrow (ca. 1.6). 1-Vinyl-2-pyrrolidone (VP) could also be polymerized in living fashion with such PNIPAAm precursor as a macroinitiator, because PNIPAAm exhibited dithiocarbamate (DC) groups at terminal ends. It was concluded that the polymerization of NIPAAm proceeded via a controlled radical mechanism in the range similar to60% of conversion. (C) 2004 Wiley Periodicals, Inc.