Metal Alkoxides as Additives for Ruthenium(II)-Catalyzed Living Radical Polymerization

Effects of additives (metal alkoxides and halides) were investigated in the RuCl 2 (PPh 3 ) 3 -catalyzed living radical polymerization of methyl methacrylate (MMA) in toluene at 80 °C. While the MMA polymerization with the RuCl 2 (PPh 3 ) 3 /CCl 4 system (CCl 4: initiator) is very slow and produces polymers with broad molecular weight distributions (MWDs), addition of metal alkoxides, such as Al(O i -Pr) 3, Ti(O i -Pr) 4, and Sn(O i -Pr) 4, accelerated the polymerization to produce polymers with controlled molecular weights and narrow MWDs. Metal chlorides such as SnCl 4 and TiCl 4 were not effective additives. According to NMR and cyclic voltammetric analyses, Al(O i -Pr) 3 does not interact with monomer or the polymer termini (∼∼∼C−Cl and ∼∼∼C • radicals) but interacts with the ruthenium complex, or more likely, its higher oxidation state Ru(III) species.