The synthesis of well-defined heteroarm star-branched polymers having poly(BMA) arms by the coupling reactions of living anionic polymers of tert-butyl methacrylate ((t)BMA) with chain-functionalized polymers with a definite number of benzyl halide moieties was described. The reaction of living anionic poly(BMA) bearing potassium countercation with benzyl bromide-functionalized polystyrenes proceeded readily and quantitatively in THF at - 40 degreesC for 1 h and - 78 degreesC for 5 h, respectively. Similarly heteroarm star-branched polymers of AB(2), AB(3), AB(4), A(2)B(4), and ABC(4) types with well-defined architectures were successfully synthesized. On the other hand, the same living poly(BMA) was sluggish to react with benzyl chloride-functionalized polystyrenes, requiring 168 h to achieve quantitative formation of AB(4) star polymer. Moreover, no reaction occurred between living poly(BMA) bearing lithium countercation in the presence of LiCl and benzyl chloride-functionalized polystyrene in THF at - 78 degreesC for 168 h.