Preparation of amphoteric N,O‐carboxymethyl hydroxypropyl chitosan by a two‐step reaction

A novel N,O-carboxymethyl hydroxypropyl chitosan (HPCMS) derivative was prepared by a two-step reaction. Water-soluble hydroxypropyl chitosan (HPCS) with a degree of substitution of hydroxypropyl higher than 0.8 was first synthesized by the reaction of chitosan (CS) with propylene oxide (PO) with alkali as a catalyst. Then, amphoteric chitosan derivatives (HPCMS) with a degree of substitution of carboxymethyl ranging from 0.42 to 1.38 were prepared by the reaction of HPCS with chloroacetic acid in an aqueous solution with alkali as a catalyst. The structures of the polymers were characterized by Fourier transform infrared spectroscopy and NMR; this showed that the hydroxypropylation mainly occurred on the OH groups at the C-6 of CS in the reaction of CS with PO. In the reaction of HPCS with chloroacetic acid, both the OH and NH2 groups of HPCS were susceptible to the carboxymethylation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 40460.