Core crosslinked star (CCS)-polymers with water-soluble arms composed of poly(N-hydroxyethylacrylamide) (PHEAA) are described. N-Hydroxyethylacrylamide was polymerized by the atom transfer radical polymerization consisting of ethyl 2-chloropropionate, copper(I) chloride (CuCl), and tris[2-(dimethylamino)ethyl]amine in an ethanol/water mixed solvent at 20 degrees C. The obtained PHEAA-arms were subsequently coupled using N,N'-methylenebisacrylamide as the crosslinking agent and sodium L-ascorbic acid (AscNa) as the reaction activator. A total of 17 representative coupling reactions with diverse conditions are discussed together with the characterizations of the products mainly by size exclusion chromatograph equipped with the multiangle laser light scattering detector (SEC-MALS). Consequently, the coupling reactions provided CCS-polymers with PHEAA-arms (CCS-PHEAAs) having weight averaged-molecular weights determined by SEC-MALS (M-w,M-MALS) ranging from 63.8 kg mol(-1) to 832 kg mol(-1), which corresponded to the average arm-number (N-arm) ranging from 4.1 to 42, respectively. CCS-PHEAA with the M-w,M-MALS of 250 kg mol(-1) was isolated and characterized by small angle X-ray scattering measurements in 0.05 M NaNO3 aq. at 25 degrees C, which was shown to possess a star-shaped structure and exist as single molecules with a radius of gyration at the infinite dilution condition (< R-g(2)>(1/2)(z,0)) of 74 +/- 4 angstrom. (C) 2012 Wiley Periodicals, Inc.