In iniferter-based photocontrolled radical polymerization optimal irradiation wavelength was examined for precise molecular design of star vectors, which can function as high-performance gene carriers. Monochromatic light in the range from 330 to 400 nm with the interval of about 10 nm was irradiated to tetrafunctional iniferter, 1,2,4,5-tetrakis(N,N-diethyldithiocarbamylmethyl)benzene, in the presence of N,N-dimethyaminopropylacrylamide (DMAPAAm), as a model monomer, in toluene. In all wavelengths tetrabranched polymers were produced except for 400-nm-irradiation. The highest conversion reaching to about 35% was observed at the wavelength of 370 nm after only 40 min of irradiation. There was no further increase in conversion by combination with another two wavelengths. HPLC analysis and NMR spectra showed that the polymerization at the optimal wavelength of 370 nm was occurred in a living manner with the ability to control the chain length (from about 5000 to 40,000) having very narrow polydispersity (about 1.6) by changing of the irradiation time, the intensity, and the monomer concentration. (c) 2008 Wiley Periodicals, Inc.