A new type of temperature-sensitive polymer systems based on mixtures of poly(acrylic acid) (PAA) and poly(diallyldimethylammonium chloride) (PDADMAC) in strongly acidic aqueous medium is described. The mixtures exhibit reversible separation into two liquid phases upon a decrease in temperature. The phase separation is induced by the intermolecular binding between PAA and PDADMAC due to ion dipole interactions between protonated carboxylic groups of PAA and quaternary nitrogen atoms of PDADMAC. Molecular and hydrodynamic characteristics of the interpolymer complexes are probed by static and dynamic light scattering.