SELECTIVE GRAFTING OF BLOCK-COPOLYMERS

Synthesis of nonpolar block copolymers selectively grafted in one bloc k with 4-methylstyrene is described, using a novel two-step method: (i ) multisite metalation of the more reactive block by a superbase, prep ared from 3-(lithiomethyl)heptane and potassium tert-pentoxide, and (i i) use of the metalated intermediate as a multifunctional initiator fo r anionic ''grafting from'' 4-methylstyene. Various degrees of graftin g (up to ca. 50%) were obtained in the reactive block, Also, other cha racteristics of the grafted block copolymers may be changed in a wide range, such as type and length of starting blocks or structure and len gth of the introduced grafts. Thus, a great variety of polymeric struc tures 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 Exc lusion chromatography coupled with concentration (RI and UV), viscosit y, and light scattering detectors.