Two routes for the synthesis of star block copolymers having exactly two arms of polyisoprene (PI) and two of polybutadiene (PB) are described. The first route starts by condensing one molecule of silicon tetrachloride with two of poly(isoprenyl)lithium which has been end-capped by a few units of styrene. The second route starts by linking two poly(isoprenyllithium) chains with one molecule of silicon tetrachloride at a suitably reduced temperature. Both routes are completed by reaction of the two-armed intermediate (PI)(2)SiCl2 with an excess of poly(butadienyllithium). The resulting (PI)(2)Si(PB)(2) star polymer was purified by fractionation. The reaction steps were monitored by size exclusion chromatography and the products characterized by low-angle laser light scattering, osmometry, and NMR.