The composition and phase diagram of aqueous two-phase systems (ATPSs) of urethanized polyvinyl alcohol (UPVA) and a series of ionic co- and terpolymers (IPs) of pH-responsive hydrophilic diallylammonioethanoate, 0-3mol% hydrophobic dodecyldiallylammonium chloride, and SO2 have been studied for the first time. The presence of unquenched nitrogen valency in the repeat units of the IPs permitted the change of the charge types and their densities in the polymer chain. The effects of zwitterionic (Z±) and anionic (A-) charge densities on the polymer backbone, salt (NaCl) concentration, and hydrophobe content on the phase diagrams were investigated. The presence of the hydrophobe in the polymer shifted the binodal downward; magnitude of the shift increased with the increase in the hydrophobe content. The phase separation happened at relatively low total polymer concentrations (much below than 10%), which could be useful in separation and purification of biomaterials.