Amphiphilic, thermosensitive ruthenium(II)-bearing star polymer catalysts: One-pot synthesis of PEG armed star polymers with ruthenium(II)-enclosed microgel cores via metal-catalyzed living radical polymerization

Amphiphilic and thermosensitive star polymers with Ru(II) complex - encapsulating microgel cores were directly synthesized in high yield via RuCl2(PPh3)(3)-catalyzed living radical polymerization. For the solvo- and thermal responsiveness, the arms stem from a block copolymer of poly(ethylene glycol) methyl ether methacrylate (PEGMA) with a small amount of methyl methacrylate. For the metal encapsulation into the core, a phosphine-ligand monomer [CH2 = CH(C6H4)PPh2] was "copolymerized" with a divinyl compound (linking agent); upon block polymer formation, in situ addition of these two components induced the linking reaction of the arm chains and, subsequently, the formation of Ru(II)-bearing microgels (cores) via ligand exchange between the triphenylphoshines in the original catalyst and the pendent phosphines in the core network. Thus, the hydrophobic catalyst [RuCl2(PPh3)(3)] for polymerization was in situ transformed into an amphiphilic core-bound catalyst. The star polymers with different Ru(II) contents were prepared by changing the ratio of the ligand monomer to the living end (or the initiator). Even after isolation and exhaustive purification, the polymers colored dark red-brown and accordingly exhibited UV - vis absorptions similar to those of RuCl2(PPh3)(3), confirming the encapsulation of Ru(II) complexes into the core, from which the Ru(II) content was estimated in the range of 24-39 mu mol/g of polymer, or 35-60 mol % of the originally added catalyst. The products were further characterized by SEC-MALLS in DMF: f (arm number) = 19-53 per polymer; M-w = 7.7 x 10(5) to 2.2 x 10(6); and R-z (radius of gyration) = 15-22 nm. The PEG-armed star polymers were also found to be amphiphilic (soluble in both alcohols and water) and thermosensitive (UCST near 30 degrees C in 2-propanol).