N-heterocyclic Carbene Containing Homogeneous Ru Catalyst for Aqueous Atom Transfer Radical Polymerization of Water-soluble Vinyl Monomers

Abstract

This report presents aqueous atom transfer radical polymerization (ATRP) of commonly used acrylate monomers in the presence of N-Heterocyclic carbene (NHC) containing homogeneous Ru catalyst in neat water. The newly synthesized Ru catalyst includes NHC, which possesses poly(ethylene glycol) (PEG) as a water-soluble component and benzylidene. The water-soluble Ru catalyst enables the polymerization of acrylamide, [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA), and PEG methyl ether methacrylate. Polymerization with this new catalyst displayed typical ATRP behavior such as a low PDI, a direct linear relationship between molecular weight and conversion, and first-order kinetics. The polySBMA (Mn 335.5 kDa and PDI 1.66) was prepared with 91% conversion at 6 h of reaction time with 0.05 mol% catalyst loading in neat water ([catalyst]:[monomer] = 1:2000 at 80 °C). Without the Ru catalyst, the thermally initiated polymerization displayed uncontrolled polymerization (e.g., non-linear kinetics, high PDI, and too fast or slow polymerizations). The Ru catalyst also demonstrated ATRP of the PEG methyl ether methacrylate in an organic solvent, acetonitrile. More detailed studies of initiator amount, solvent concentration, and catalyst amount effects were performed. In turn, the new ATRP will add prominent value to the polymer science field as an initial example of Ru-benzylidene catalyzed ATRP in neat water. Additionally, this will promote various applications of environmentally benign polymerization as well as applications in the biomedical field with high-cost efficiency.