Polystyrene was directly azidated in 1,2-dichloroethane or chlorobenzene using a combination of trimethylsilyl azide and a hypervalent iodine (111) compound, (diacetoxyiodo)-benzene. 2D NMR HMBC experiments indicated that the azide groups were attached to the polymer backbone and also possibly to the aromatic pendant groups. The amount of introduced azide groups was estimated by semi-quantitative IR spectroscopy and elemental analysis. Approximately 1 in every 11 styrene units could be modified by using a ratio of hypervalent iodine compound to trimethylsilyl azide to styrene units of 1:2.11 at 0 degrees C for 4 h followed by heating to 50 degrees C for 2 h in chlorobenzene. The azidated polymers were further used as backbone precursors in the synthesis of polymeric brushes with hydrophilic side chains via a copper-catalyzed click grafting-onto reaction with poly(ethylene oxide) monomethyl ether 4-pentynoate. (C) 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 966-974, 2010