The synthesis of well-defined heteroarm star-branched polymers having poly( t 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( t BMA) bearing potassium countercation with benzyl bromide-functionalized polystyrenes proceeded readily and quantitatively in THF at -40 o C for 1h and -78 o C for 5h, 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( t BMA) was sluggish to react with benzyl chloride-functionalized polystyrenes, requiring 168h to achieve quantitative formation of AB 4 star polymer. Moreover, no reaction occurred between living poly( t BMA) bearing lithium countercation in the presence of LiCl and benzyl chloride-functionalized polystyrene in THF at -78 o C for 168h.