A hydrophilic monomer (diallyldimethylammonium chloride), a hydrophobic monomer (diallyloctadecylammonium chloride), and sulfur dioxide are cycloterpolymerized in dimethylsulfoxide using azobisisobutyronitrile as the initiator to afford water-soluble cationic polyelectrolytes having a five-membered cyclic structure on the polymeric backbone. The molecular weights of the polymers containing varying amounts of the hydrophobic monomer (0-7.5 mol %) are determined by light-scattering experiments. The solution properties of the series of cationic polyelectrolytes are investigated by viscometric techniques. A polymer concentration (C*(HA)) Of < 1 g/dL is required for the manifestation of hydrophobic associations in these terpolymers containing C-18 hydrophobic pendents. This is a notable improvement over the C*(HA) values (ca. 15-1.7 g/dL) for the associating cyclopolymers having a pendant length of C10 to C14. The polymer solutions exhibit a sharp increase in viscosity with increasing polymer concentrations in salt-free as well as salt-added solutions. The presence of sodium chloride is shown to enhance the hydrophobic association tremendously. (c) 2005 Wiley Periodicals, Inc.