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N,N-Diallylammoniomethanesulfonate, a new zwitterionic monomer having a sulfobetaine (SB) motif, has been synthesized by reacting diallylamine with formaldehyde and sodium bisulfite. While the monomer underwent cyclopolymerization to give the unstable polysulfobetaine (PSB) in low yields, copolymerization with sulfur dioxide gave the stable PSB/SO2 copolymer in excellent yields. The polymers, as a consequence of having unquenched nitrogen valency in the repeating units, are pH-responsive. The PSB/SO2 copolymer, upon treatment with sodium hydroxide, was converted into a water-soluble anionic polyelectrolyte (APE). The strong zwitterionic interactions inherent in the PSB/SO2 made it insoluble in salt-free water; the presence of large concentration (>3M) of low molecular weight salts (e.g., NaCl, KI etc,) was required to neutralize the intragroup zwitterionic interactions and promote dissolution. The PSB/SO2 represents the first example of a sulfobetaine polymer having a single methylene spacer separating the charge centers. The stability of the copolymer is explained in terms of electron density on the nitrogens. POLYM. ENG. SCI., 53:2378–2388, 2013. © 2013 Society of Plastics Engineers