Understanding Copper-Based Atom-Transfer Radical Polymerization in Aqueous Media

Abstract

This study investigates the mechanism of copper(I)-mediated “living” atom-transfer radical polymerization (ATRP) in aqueous media. It is shown that the ATRP apparent rate constant for polymerization of methoxy-capped oligo(ethylene glycol) methacrylate (OEGMA) in water (kpapp) at room temperature correlates with the redox potential (E1/2) of the copper complexes. The results are discussed along with previously published results on the kinetics for bulk polymerization of methyl acrylate at 60 °C with the redox potentials measured in MeCN. The faster ATRP kinetics in water can mainly be attributed to a higher equilibrium concentration of propagating radicals [R•] and to solvent effects on the rate of propagation kp. It is shown that [R•] can be calculated from the redox properties of the alkyl halide and the copper complex. The values of [R•] in MeCN/bulk and in H2O were determined to be 8.2 × 10-8 and 6.3 × 10-5 M, respectively. The respective kp values are in good agreement with the literature values (3.6 × 103 M-1 s-1 for OEGMA in water and 2.5 × 103 M-1 s-1 for methyl acrylate in bulk).