The zwitterionic monomer ethyl 3 (N N-diallylammonio)propanephosphonate was cyclopolymenzed in aqueous solutions using t butylhydroperoxide or ammonium persulfate as initiators to afford a polyphosphonobetaine (PPB) The pro tonation of P(=O)OEtO- and deprotonation of -NH+ groups in PPB by HCI and NaOH gave the corresponding cationic poly phosphononic acid (CPP) and anionic polyphosphonate (APP) The presence of two pH responsive functionalities in APP has led to establish the equilibria APP reversible arrow PPB reversible arrow CPP the position of which very much dictates the viscosity behavior of its aqueous solution The PPB demonstrated antipolyelectrolyte viscosity behavior however in contrast to many polycarbo and polysulfo betaines it was found to be soluble in salt free water as well as in salt added solutions Basicity constant (K-1) of the amine group in APP as determined by potentiometnc tech nique were found to be apparent and as such followed the modified Henderson Hasselbalch equation The study demon strated a correlation between the basicity constants and viscosity values (c) 2010 Wiley Periodicals Inc J Polym Sci Part A Polym Chem 48 5693-5703 2010