Synthesis and characterization of tris(2,2′-bipyridine)ruthenium(II)-centered polystyrenes via reversible addition-fragmentation chain transfer (RAFT) polymerization

A novel bipyridine-functionalized dithioester, 5,5'-bis(thiobenzoylthiomethyl)-2,2'-bipyridine (3), was first synthesized through a simple ester exchange reaction with the commercially available dithioester, carboxymethyl dithiobenzoate (CMDB), and further used as a RAFT agent in bulk polymerization of styrene for the synthesis of well-defined bipyridine-centered polystyrene polymers. The molecular weight is well-controlled, and also the molecular weight distribution remains quite narrow. This shows that the novel bipyridine-functionalized dithioester 3 is an efficient RAFT agent. More importantly, the good agreement between theoretical and H-1 NMR-determined molecular weights indirectly indicates that almost all of the polymer chains are centered by the bipyridine functional groups derived from the new RAFT agent. Two of the bipyridine-centered polystyrene polymers were further complexed with ruthenium(II) ions to produce tris(bipyridine)ruthenium(II)-centered polystyrene metallopolymers. The metallopolymers were characterized by UV-vis, fluorescence, size exclusion chromatography (SEC), and differential scanning calorimetry (DSC) techniques. The characterization data show that tris(bipypridine)ruthenium(II) ions have been successfully incorporated into the center of polymer chains.