Synthesis And Stimuli-responsive Properties Of Chitosan-based Zwitterionic Polyelectrolyte

Chitosan, due to its wonderful biocompatibility and biodegradability, has the extensive and potential applications in the fields of drug, food, pharmaceutical and cosmetic formulations. The water-soluble and stimuli-responsive chitosan-based derivatives exhibit novel properties in biosensor, drug delivery systems, protein recognition and separation due to its capacity of response to the environmental variation.This study focuses at the synthesis of pH-, salt- and temperature-responsive chitosan-based zwitterionic polyelectrolytes and investigation of their solution properties. These derivatives were characterized by NMR, FT-IR, DSC, TGA and XRD studies, and the solution properties were investigated by various measurements including viscosity, turbidity, UV-vis absorbance, temperature-variable 1H NMR, surface tension and distribution of diameter. The main results were given as follows: (1) N-carboxyethyl chitosan (CECTS) was synthesized by Michael reaction of chitosan with acrylic acid, and the aqueous solution properties were studied. 1H NMR analysis of CECTS under various solution pH shows that different structural part in CECTS exhibits different solubility in water due to the combined driving-force of hydrophilicity/hydrophobicity, Coulombic force and hydrogen bond. The results of turbidity measurements illustrate the typical polyzwitterionic properties of CECTS which display clear isoelectric point (IEP) and the critical salt concentration (CSC). While CECTS exhibits typical cationic and anionic polyelectrolyte effects for both solutions at pH 3 and 9.5 respectively, where, the relative viscosity of aqueous solution decreased with the increase of NaCl concentration.(2) The esterification of P2O5 with (2-hydroxy)ethyl acrylate acquired mono-(2-acryloyloxyethyl) phosphate (MAEP). The Michael addition of MAEP and amino group in chitosan prepared chitosan-based derivatives with phosphate groups (NPCPA). FT-IR and NMR were employed to characterize NPCPA. The effect of [MAEP]:[-NH2], solution pH, reaction time and reaction temperature on the degree of substitution (DS) of NPCPA was studied, and the results show that: the maximum DS was attained when keeping [MAEP]:[-NH2] as 4:1, solution pH at 3.12 , reaction time and temperature as 3 h and 36℃respectively, showing a relatively high reactivity. NPCPA exhibits polyelectrolyte or anti-polyelectrolyte effect in various solution pH. The viscosity measurements of NPCPA with solution pH as 10.5 illustrate its...