The quaternary ammonium monomer 1,1-diallyl-4-methoxycarbonylpiperidinium chloride was synthesized in good yield. On polymerization in water using t-butylhydroperoxide as initiator, a cationic polyelectrolyte (CPE) with a five-membered cyclic structure on the polymeric backbone was obtained. On acid hydrolysis, followed by basification, the CPE gave the corresponding polybetaine (PB). The solution properties of these polymers were investigated by potentiometric and viscometric techniques. The PB demonstrated "antipolyelectrolyte'' behavior. The basicity constant of the carboxylate functionality in the polyzwitterionic polymers was 'apparent' in a 0.1 N NaCl solution and followed the modified Henderson-Hasselbalch equation. It was found that as the degree of protonation (alpha) of the whole macromolecule increases, the protonation of the amine nitrogen becomes increasingly more difficult. Unlike other polyzwitterions/polybetaines, the PB was soluble in salt-free water. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 1477-1485, 2011