Aqueous Atom Transfer Radical Polymerization (ATRP) with Homogeneous Ruthenium Benzylidene Catalyst

An important recent issue of polymer synthesis is a green polymerization that uses water as a solvent due to sustainability and environmental concern. Desirable ligand design is important for a highly active homogeneous aqueous transition metal catalyst. Ruthenium (Ru) is the first transition metal used as a catalyst for modern controlled/living radical polymerizations. In particular, Ru- N-heterocyclic carbene (NHC) catalyst is an effective catalyst in not only ATRP but also metathesis reaction. In this research, we have synthesized NHC containing homogeneous Ru catalyst to perform ATRP of commonly used vinyl monomers, acrylate derivatives. The NHC of catalyst possesses poly(ethylene glycol) (PEG) as a water-soluble component. Another important part of the catalyst is Ru benzylidene (Grubbs 2nd generation analog) which leads ATRP of vinyl monomers as well as metathesis reactions. The new Ru catalyzed polymerization of Acrylamide, [2-(Metha cryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide(SBMA), and PEG methyl ether methacrylate (PEGMEMA) demonstrated typical ATRP behavior showing low molecular weight distribution, linear increase of molecular weights with conversion, and first-order kinetics. The used alkyl bromide initiator was water-soluble PEG methyl ether 2-bromoisobytyrate. Specifically, polyacrylamide of molecular weight 341.8 kDa (PDI: 1.25) was prepared with 95% conversion at 6 hours of reaction time (reaction temperature 80 ℃) with 0.05 mol% catalyst loading ([catalyst]:[monomer] = 1:2000). Unlike the Ru-catalyzed ATRP, thermally-initiated polymerization without catalyst showed completely uncontrolled polymerization (non-linear kinetics) of acrylamide monomer. Additional solvent, acetonitrile, and zwitterionic monomer ([2-(Methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide) methacrylate monomer also underwent ATRP in the presence of the new Ru catalyst. The more detailed studies of temperature, initiator amount, solvent concentration, catalyst amount effects are completed. The new ATRP will be greatly advantageous to polymer science as an initial example of Ru-catalyzed ATRP in neat water which has significant benefits of inexpensive, non-toxic, and readily available solvent features.