Poly(2-vinylpyridine)-based star-shaped polymers. Synthesis of heteroarm star (AnBn) and star-block (AB)n copolymers

Heteroarm star copolymers bearing poly(2-vinylpyridine) and polystyrene arms (A n B n type) were synthesized by a three-step anionic polymerization method. Polystyrene arms are synthesized first, and they are used to initiate the polymerization of a small amount of divinylbenzene, yielding polystyrene star molecules bearing a number of active sites within its cores. In a subsequent step poly(2-vinylpyridine) arms are growing from the cores. Poly(2-vinylpyridine)-block-poly(tert-butyl acrylate) star block copolymers [(AB) n type] were also prepared using the same synthetic route. In this case, short polystyryllithium is used to build grafted poly(DVB) cores. These living plurifunctional initiators can easily polymerize 2-vinylpyridine and subsequently tert-butyl acrylate, yielding star molecules bearing diblock copolymers as arms. The short polystyrene grafts of the core can be neglected and the star molecules are considered of the (AB) n type. These star polymers have been characterized adequately and shown to exhibit rather well-defined structures. The advantages and the drawbacks of the method are discussed.