Synthesis of nonpolar block copolymers selectively grafted in one block with 4-methylstyrene is described, using a novel two-step method : (i) multisite metalation of the more reactive block by a superbase, prepared from 3-(lithiomethyl)heptane and potassium tert-pentoxide, and (ii) use of the metalated intermediate as a multifunctional initiator for anionic "grafting from" 4-methylstyene. Various degrees of grafting (up to ca. 50%) were obtained in the reactive block, Also, other characteristics of the grafted block copolymers may be changed in a wide range, such as type and length of starting blocks or structure and length of the introduced grafts. Thus, a great variety of polymeric structures is available by this method. Molecular weight, molecular weight distribution, and molecular size of the copolymers in tetrahydrofuran were determined by static and dynamic light scattering and by size Exclusion chromatography coupled with concentration (RI and UV), viscosity, and light scattering detectors.