Aqueous radical polymerization of N,N-dimethylacrylamide redox-initiated by aerobically catalytic oxidation of water-soluble tertiary amines

Abstract

Catalytic oxidation of water-soluble tertiary amines by complexes of CuII, FeIII and CoII was utilized to initiate radical polymerization of N,N-dimethylacrylamide (DMAAm) in aqueous solution at 70–80 °C. The oxidation of tertiary amines by CuII was studied by proton nuclear magnetic resonance spectroscopy and online ultraviolet–visible spectrophotometry. The polymerization kinetics was monitored by gas chromatography, and molecular weight of the PDMAAm was measured by gel-permeation chromatography coupled with multi-angle laser light scattering. Oxidation of tertiary amines occurs predominantly via formation of Calpha·radicals to initiate polymerization of electron-deficient monomers and N-dealkylation, and redox equilibrium between CuI/L and CuII/L is established at a faster rate in aqueous media. FeIII and CuII complexes are efficient catalysts as each catalyst molecule could generate above 10 propagating radicals in 5 h, while CoII complex might involve in oxidation of tertiary amines in non-radical pathway, leading to a low catalytic efficiency. Water-soluble tertiary amines such as N,N-dialkylethanolamine (alkyl = methyl, ethyl etc.) are reducing agents of a higher activity in aqueous media than those primary or secondary analogues. Our strategy renders it possible to prepare polymer of alpha-amino functionality via one-pot process from commercially available commodity reagents under practical conditions with negligible catalyst residue.