Improvement of the control over SARA ATRP of 2-(diisopropylamino)ethyl methacrylate by slow and continuous addition of sodium dithionite

Abstract

The kinetics and detailed mechanism of SARA ATRP of 2-(diisopropylamino)ethyl methacrylate (DPA) were investigated. Supplemental activator and reducing agent (SARA) atom transfer radical polymerization (ATRP) using sodium dithionite (Na₂S₂O₄) was used to create well controlled polymers of PDPA. The influence of the initiator, solvent, structure and concentration of the catalyst was studied, and the ratios of Na₂S₂O₄ were adjusted to optimize the polymerization. Well controlled polymers required Na₂S₂O₄ to be slowly and continuously fed to the reaction mixture, with 500 parts per million (ppm) of CuBr₂ with tris(2-dimethyamino)amine (Me₆TREN) as a ligand. The initial content of Na₂S₂O₄ in the reaction mixture, the feeding rate and the Cu catalyst concentration were optimized to provide polymers with narrow molecular weight distribution (M_w/M_n < 1.15) at high monomer conversion (∼90%). Interestingly, the results revealed that when tris(2-pyridylmethyl)-amine (TPMA) was used as a ligand, the amount of copper required to achieve similar control of the polymerization could be decreased 5 times. This system was successfully extended to the polymerization of oligo(ethylene oxide) methyl ether methacrylate (OEOMA). The high conversion and preservation of the chain-end functionality allows the direct synthesis of POEOMA-b-PDPA block copolymers. The low catalyst concentrations and benign nature of Na₂S₂O₄ make this SARA ATRP method attractive for the synthesis of well controlled water soluble polymers for biomedical applications.