Synthesis and cyclopolymerization of diallylammoniomethanesulfonate

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/SO ₂ 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.