Heteroarm star-shaped polymer, (polystyrene)(n)-[poly(ethyl acrylate)](m) [(PS)(n)-(PEA)(m)], was synthesized in three steps. In the first step, star-shaped polystyrene, (PS)(n), was synthesized by the arm-first method via atom transfer radical polymerization (ATRP) using a preformed PS macroinitiator, which was obtained by ATRP of styrene with ethyl 2-bromoisobutyrate as the initiator, in the presence of divinyl benzene (DVB). In the microgel core of (PS)(n), there were not only a number of active initiating sites for ATRP, but also some unreacted vinyl groups. Then, in the second step, the residual vinyl groups were converted to 1-bromoethylbenzene groups by hydrobromination. In the last step, heteroarm star-shaped polymer, (PS)(n)-(PEA)(m), where the arm number of PEA was greater than that of PS, was prepared by ATRP of ethyl acrylate using the hydrobrominated (PS)(n) as the macroinitiator from 1-bromoethylbenzene initiating sites, obtained by both the addition of linear PS macroinitiators to vinyl groups of DVB and the hydrobromination of residual vinyl groups. (c) 2006 Elsevier Ltd. All rights reserved.