Three kinds of new substituted polystyrene derivatives functionalized with two or four benzyl bromide moieties in every monomer unit were successfully synthesized via living anionic polymerizations, functionalization reactions with the 1,1-diphenylalkyl anion prepared from 1,1-bis(3-tert-butyldimethylsilyloxymethylphenyl)ethylene and sec-BuLi, and transformation reactions with LiBr-(CH3)(3)SiCl. These polymers were precisely controlled in chain length and quantitatively functionalized with benzyl bromide moieties. The synthesis of well-defined densely branched polystyrenes and graft copolymers carrying two or more branches in all repeating units were attempted using the coupling reactions of such benzyl bromide-functionalized polystyrenes with living anionic polymers of styrene, isoprene, and tert-butyl methacrylate in THIP at -40 degreesC. The coupling reaction was found to proceed quantitatively under appropriate conditions to afford densely branched polymers carrying two branches in each repeating unit. In contrast, the coupling reaction of the polystyrene functionalized with four benzyl bromide moieties with living anionic polymers of styrene was incomplete and only two polystyrene chains could be introduced in each repeating unit. The structures of the resulting branched polystyrenes were investigated by intrinsic viscosity measurement. These polymers may adopt starlike rather than rodlike structures in toluene as evidenced by their g' values.