A combination of nitroxide-mediated radical polymerization and living anionic polymerization was used to synthesize a series of well-defined graft (co)polymers with "V-shaped" and "Y-shaped" branches. The polymer main chain is a copolymer of styrene and p-chloromethylstyrene (PS-co-PCMS) prepared via nitroxide-mediated radical polymerization. The V-shaped branches were prepared through coupling reaction of polystyrene macromonomer, carrying 1,1-diphenylethylene terminus, with polystyryllithium or polyisoprenyllithium. The Y-shaped branches were prepared through further polymerization initiated by the V-shaped anions. The obtained branches, carrying a living anion at the middle (V-shaped) or at the end of the third segment (Y-shaped), were coupled in situ with pendent benzyl chloride of PS-coPCMS to form the target graft (co)polymers. The purified graft (co)polymers were analyzed by size exclusion chromatography equipped with a multiangle light scattering detector and a viscometer. The result shows that the viscosities and radii of gyration of the branched polymers are remarkably smaller than those of linear polystyrene. In addition, V-shaped product adopts a more compact conformation in dilute solution than the Y-shaped analogy. (C) 2007 Wiley Periodicals, Inc.