Modified chitosan derivatives with different degrees of substitution varying from 0.17 to 0.96 were synthesized by the heterogeneous reaction of chitosan with 3-chloro-2-hydroxy propanesulfate in a neutral aqueous solution. The modified chitosans with a degree of substitution higher than 0.36 were soluble in water, whatsoever the pH. The structures of the polymers were characterized by Fourier transform infrared and H-1-nuclear magnetic resonance spectroscopies. The potentiometric titration revealed that the modified chitosan had an isoelectric point at around pH = 5.7, and its rheological behaviors in aqueous solution were studied under different conditions. The results showed that the modified chitosan had typical polyampholyte characteristics, which exhibited polyelectrolyte effect at pH = 1.7 or 13 and antipolyelectrolyte effect at pH = 8. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 3382-3387, 2009