Copolymers of N,N-diallyl-N,N-dimethylammonium chloride (DADMAC) and the zwitterionic monomer 3-(N,N-diallyl-N-methylammonio)propanesulfonate (DAMAPS) have been prepared in a 0.5 M NaCl aqueous solution using 2-hydroxy-1-[4-(hydroxyethoxy)phenyl]-2-methyl-1-propanone (Irgacure 2959) as the free-radical photoinitiator. The feed ratio of DADMAC:DAMAPS was varied from 100:0 to 0:100 mol % with the total monomer concentration held constant at 2.5 M. C-13 NMR data indicate that the resulting polymers maintain the five-membered ring structure in the cia conformation common to diallylammonium salts. Reactivity ratio studies indicate that the sulfobetaine monomer is incorporated randomly along the polymer backbone; Laser light scattering provided molecular weights and second virial coefficients, which varied from 5.16 x 10(4) to 8.42 x 10(4) and 5.54 x 10(-4) to 1.89 x 10(-4) mt mol g(-2), respectively. Solution behavior is dependent upon ionic strength as determined by low shear viscosity and dynamic light scattering experiments. For cyclocopolymers containing <40 mol % sulfobetaine, classical polyelectrolyte behavior is shown by viscosity decreases with increasing ionic strength. However, for polymers containing greater than or equal to 40 mol % sulfobetaine, chain expansion occurs as the ionic strength is increased above that required for the Donnan equilibrium.