Facile Synthesis of Acidic Copolymers via atom transfer radical polymerization in aqueous media at ambient temperature

There is growing interest in atom transfer radical polymerization (ATRP) which, unlike living ionic polymerizations, is remarkably tolerant of functional groups.1,2 With regard to hydrophilic monomers, Matyjaszewski and co-workers have reported the well-controlled (co)polymerization of 2-hydroxyethyl acrylate3 in aqueous media at 90 °C, 2-(dimethylamino)ethyl methacrylate4 at 23 °C in bulk or nonaqueous media, and 4-vinylpyridine5 in alcoholic media at 40 °C. We have recently described the facile polymerization of monomethoxy-capped oligo(ethylene oxide) methacrylate6 [OEGMA] in aqueous media at 20 °C using a similar protocol. ATRP of acidic monomers have generally proved more problematic. For some time, it was believed that protecting group strategies were necessary since carboxylic acid-based monomers such as methacrylic acid or acrylic acid formed insoluble complexes with the copper catalyst if ATRP was attempted in nonaqueous media.7 However, we recently demonstrated that methacrylic acid8 could be polymerized directly in its sodium salt form by ATRP in aqueous solution. Although an important “proof of concept” experiment, the conversion of sodium methacrylate to polymer was both slow and substantially incomplete, with yields of only 70−80% being obtained after 21 h at 90 °C. Herein we describe the efficient, well-controlled (co)polymerization of a second acidic monomer, sodium 4-vinylbenzoate [NaVBA], via ATRP in aqueous media (see Figure 1). In contrast to sodium methacrylate, excellent yields are obtained in very short reaction times even at 20 °C