The homopolymerization of sodium 4-styrenesulfonate (NaStS) in both aqueous and water/methanol solutions at 20 degreesC using atom transfer radical polymerization (ATRP) is described. Syntheses conducted using a sodium 4-bromomethylbenzoate initiator were poorly controlled in water but reasonably well-controlled in 1:1 water/methanol mixtures, with 3:1 water/methanol mixtures exhibiting intermediate behavior. In 1:1 water/methanol mixtures aqueous GPC analyses indicated polydispersities as low as 1.26 and conversions reached 80-90% within 18-20h at 20 degreesC. Self-blocking experiments were conducted in 1:1 water/methanol mixtures, with the chain-extended NaStS polymers exhibiting uniniodal GPC traces but relatively high polydispersities (M-w/M-n = 1.61). The use of poly(ethylene oxide)-based (PEO) macro-initiators yielded novel PEO-NaStS diblock copolymers of low polydispersity. Diblock copolymer syntheses via sequential monomer addition were less satisfactory, although one example of a polydisperse pH-responsive diblock copolymer was obtained. (C) 2003 Elsevier Ltd. All rights reserved.