The amine salt N,N-diallyl-N-5-carbomethoxypentylammonium chloride was copolymerized with sulfur dioxide in dimethyl sulfoxide with ammonium persulfate or 2,2'-azobisisobutyronitrile and afforded a cationic polyelectrolyte (CPE) with a five-membered cyclic structure on the polymeric backbone. The CPE, upon acidic hydrolysis of the pendent ester groups, gave a corresponding cationic acid salt (CABS) having the equivalent of chloride salt of 6-N,N-diallylammoniohexanoic acid as the monomeric unit. The CAS was converted into an anionic polyelectrolyte (APE) and a polybetaine (PB), having the monomeric unit equivalent of sodium 6-N,N-diallylaminohexanoate and 6-N,N-diallylammoniohexanoate, by treatment with 2 and 1 equiv of base, respectively. The solution properties of APE were investigated by potentiometric and viscometric techniques. The basicity constant of the amine functionality in APE was apparent and as such followed the modified Henderson-Hasselbalch equation; the protonation of the APE became more and more difficult as the degree of protonation of the whole macromolecule increased. The compositions and phase diagrams of the aqueous two-phase systems of APE and poly(ethylene glycol) were studied. The PB was found to be insoluble in water, and this paves the way for the potential use of APE in aqueous two-phase polymer systems for protein purification and its removal and recycling by conversion into PB.