A series of star-shaped polyisoprenes (Star-PIps) were synthesized by copolymerization of isoprene as an arm monomer and a branched homopolymer of dimethyl-di-2,4-pentadienyl-(E,E)-silane (DMDPS) as a macromonomer core through the “core-first” approach catalyzed by the half-sandwich scandium complex (C₅Me₄SiMe₃)Sc(CH₂C₆H₄NMe₂-o)₂/[Ph₃C][B(C₆F₅)₄]. Due to the different activities of DMDPS in polymerization with two catalysts (C₅Me₄SiMe₃)Sc(CH₂C₆H₄NMe₂-o)₂ (Sc-1) and (C₅H₅)Sc(CH₂C₆H₄NMe₂-o)₂ (Sc-2), a series of macromonomers with varied molecular weights and numbers of pendant vinyl groups were successfully obtained. The different activities and reaction characteristics of DMDPS in the two catalytic systems were also verified in detail by computational chemistry. Star-PIps with different molecular weights from 26.2 × 10³ to 175.8 × 10³ g mol⁻¹ and arm numbers from 19 to 70 were produced when different macromonomers were used as cores. By changing the concentration of isoprene, Star-PIps with varied arm lengths were achieved.