A new kind of star-shaped block copolymer: tin-coupled polybutadiene-b-poly(styrene-butadiene) ((SB-B)(4)Sn) was synthesized by two-stage anionic polymerization technology. A novel multifunctional organo-lithium was used as initiator, and two different types of copolymers were formed, namely, S-PB-PSB and S-PB-PSB-PS, depending on the styrene content in loading solution (St%). In copolymerization, the homo-polybutadiene block was formed in the first reaction stage, and the residual blocks were formed in the second stage with the presence of tetrahydrofuran (THF). S-PB-PSB was synthesized when the St% was lower than 34.9%, otherwise S-PB-PSB-PS was generated. Nuclear magnetic resonance (NMR) results showed that the amount Of vinyl based upon the butadiene content within poly(butadiene-styrene) blocks decreased dramatically as the St% was increased. Dynamic mechanical thermal analyzer (DMTA) spectra showed broadened loss peak as the St% was increased. Transmission electron microscopy (TEM) was employed to characterize the copolymer morphology, and the results, showed different phase-separated morphologies as St%, increased. Mechanical property testing results indicated that these two copolymers met the requirements of high performance tire tread. (C) 2008 Wiley Periodicals, Inc.