Gel-Phase Synthesis and pH-Sensitive Swelling-Structure Relationships of N-Carboxyethylchitosan

Abstract

The applicability of native chitosan-based compositions is constrained by their limited solubility in weakly alkaline and neutral media, a consequence of inherent structural features. To overcome this limitation, carboxyalkylation strategies such as the gel-phase Michael synthesis of N-carboxyethylchitosan (N-CEC) were investigated with a focus on optimizing reaction parameters to enhance yield and tailor biopolymer properties. Structural confirmation of the synthesized polymers was performed via FT-IR and SEM, while elemental analysis quantified the degree of substitution (DS), which correlated with temperature in the following way: DS = 0.96–1.10 at 50 °C, 1.07–1.12 at 60 °C and 1.16–1.32 at 70 °C. Porosity measurements indicated pore sizes ranging from 50 to 200 µm in all samples; however, total porosity varied significantly, reaching a maximum of 15 % at 70 °C and decreasing to 4–10 % at lower temperatures. N-CEC exhibited pH‑dependent swelling, with minimal expansion (100–150 %) at low pH and a 2–3-fold increase at pH > 7, which was attributed to COO⁻ group formation. These findings position N-CEC as a promising material for pH-responsive applications.