A series of high-density branched polymers have been synthesized by the coupling reaction of poly(4-(3-(4-bromomethylphenyl)propyl)styrene with polymer anion comprised of two same or different polymer chains, prepared from polystyryllithium and either polystyrene or polyisoprene with 1,1-diphenylethylene chain-end functionalization. Under certain conditions, the reaction proceeded essentially quantitatively to afford the requisite extremely high-density branched polymers carrying two branch chains in each repeating unit and having M-w values of up to 3 x 10(6). Furthermore, quite new graft-block copolymers with similar high-density branched architectures could also be successfully synthesized. The resulting polymers are well-defined in branched architecture and precisely controlled in chain lengths of both backbone and branch segments. It was however observed that the reaction efficiency was significantly affected by several variables such as degrees of polymerization of the backbone polymer and polymer anion and branched and chemical structures of the polymer anion. The structures of the resulting high-density branched polymers were investigated by intrinsic viscosity measurement. These polymers may possibly adopt starlike structures in toluene as evidenced by their g' values.