Sulfobetaine homopolymers were synthesized by aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. Typically, the MASB monomer was dissolved in pure water, followed by the chain transfer agent (CTA), 4-(2carboxyethylsulfanylthiocarbonyl)sulfanyl-4-cyanopentanoic acid. The initiator, 2,2 0 -azobis[2-(2-imidazolin-2-yl)propane] was dissolved in methanol and mixed with the monomer/CTA solution. The molar ratio of monomer to CTA and initiator was [monomer] :
[CTA] : [initiator] = 100 : 1 : 0.3, and the final concentration of the monomer was set to 0.1 M. The solvent was a mixture of pure water and methanol at a volume ratio of 2 : 1. Nitrogen gas was bubbled for 30 min to remove dissolved oxygen, and the polymerization was carried out in an oil bath at 60 1C for 18 h. The polymer was purified by dialysis in pure water (MWCO = 3500) for 7 days to remove any unreacted monomer. The polymer powder was obtained by freeze-drying the purified solution. The molecular weight of the polymers was determined via gel permeation chromatography using a JASCO system (Tokyo, Japan) with TSKgel G3000PW XL and G4000PW XL columns (Tosoh Co. Tokyo, Japan). The eluent was aqueous NaNO 3 (400 mM) calibrated with PEG standards.
[CTA] : [initiator] = 100 : 1 : 0.3, and the final concentration of the monomer was set to 0.1 M. The solvent was a mixture of pure water and methanol at a volume ratio of 2 : 1. Nitrogen gas was bubbled for 30 min to remove dissolved oxygen, and the polymerization was carried out in an oil bath at 60 1C for 18 h. The polymer was purified by dialysis in pure water (MWCO = 3500) for 7 days to remove any unreacted monomer. The polymer powder was obtained by freeze-drying the purified solution. The molecular weight of the polymers was determined via gel permeation chromatography using a JASCO system (Tokyo, Japan) with TSKgel G3000PW XL and G4000PW XL columns (Tosoh Co. Tokyo, Japan). The eluent was aqueous NaNO 3 (400 mM) calibrated with PEG standards.