The zwitterionic monomer, 3-(N,N-diallyl,N-carboethoxymethylammonio)propanesulfonate, on cocyclopolymerization with sulfur dioxide in DMSO using azoisobutyronitrile as the initiator afforded the polyzwitterion (PZ) copolymer in excellent yields. The PZ on acidic hydrolysis of the ester groups led to the corresponding polyzwitterionic acid (PZA). The pH-responsive PZA on treatment with sodium hydroxide gave the new poly(eletrolyte-zwitterion) (PEZ). The solubility, viscosity behaviors, and solution properties of the salt-tolerant PZ, PZA, and PEZ were studied in detail. Like common PZs, PZ was found to be insoluble in salt-free but soluble in salt-added water. The apparent basicity constants of the carboxyl group in PEZ have been determined. As the name implies, the PEZ possesses dual type of structural feature common to both conventional anionic polyelectrolytes and PZs, and its aqueous solution behavior is found to be similar to that observed for a typical alternating anionic-zwitterionic copolymer. (c) 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013