An iron-mediated atom transfer radical polymerization with activators generated by electron transfer (AGET) ATRP was used to modify the synthetic rubber polystyrene-b-poly(ethylene-co-1-butene)-b-polystyrene (SEBS) triblock copolymer, which is the product of the hydrogenated polystyrene-b-polybutadiene-b-polystyrene (SBS) triblock copolymer precursor. The AGET ATRP reaction was carried out using the chloromethylated SEBS as the macroinitiators. FeCl(3)center dot 6H(2)O as the catalyst, tris(3,6-dioxaheptyl)amine or triphenylphosphine as the ligand, and vitamin C as the reducing agent in the presence of limited amounts air. Different grafted SEBSs were obtained using methyl methacrylate (MMA), styrene and tert-butyl acrylate as the monomers. The graft density could be adjusted by the degree of chloromethylation of SEBS. The grafting kinetics of MMA revealed that the iron-mediated AGET ATRP showed several key features of 'living' radical polymerization such as molecular weights (M(n) = 90,000-139,500 g/mol) increasing with monomer conversion and keeping narrow polydispersity (M(w)/M(n) = 1.14-1.32) for the obtained PMMAs. The composition and structures of the grafted copolymers were characterized by Fourier transform infrared spectra and (1)H nuclear magnetic resonance spectra. Crown Copyright (C) 2011 Published by Elsevier Ltd. All rights reserved.