Poly(2-vinylpyridine)-based star-shaped polymers. Synthesis of heteroarm star (A(n)B(n)) 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 poly-styryllithium 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.