A multiarm star polymer was synthesized through the grafting of oligo polyglycol with urethane chain end units onto the core of hyperbranched polyglycerol (HPG), which was obtained through the cationic ring-opening polymerization of glycidol. Samples were characterized with C-13 NMR, liquid chromatography/mass spectrometry, vapor pressure osmometry, and Raman spectroscopy. The degree of branching of HPG was 0.54, and the number of arms grafting onto HPG was 4. The urethane of the arms mainly reacted with the terminal hydroxy groups of HPG. The differences between the spin-spin relaxation times indicated that the terminal segments of the star were more flexible than those of the core. Grafting polyglycol polyurethane (soft segments of polyurethane is polyglycol) onto HPG improved its dimensional stability. (C) 2004 Wiley Periodicals, Inc.