H‐bond in chitosan‐based hydrogels

Abstract

AbstractN‐alkyl chitosan derivatives, including N‐ethyl, butyl, heptyl and lauryl forms were prepared via Schiff's base intermediates. The study of H‐bonds in chitosan‐based hydrogel was performed by DSC, NMR, XKD and PALS. The content of unfrozen bound water increases with increasing length of the alkyl side chain and the degree of substitution. The X‐ray diffraction peak centered at 2θ=26.5° is sensitive to water. The free volume enhances in the order, chitosan (CS) < N‐ethyl CS < N‐butyl CS < N‐heptyl CS << N‐lauryl CS. Moreover the free volume of the derivatives decreases as water content rises but the situation of chitosan is opposite. The dynamic properties of water molecules within the networks were studied through the variation of the proton line width in the 1H‐NMR spectrum. The proton line width of the water peak of N‐alkyl chitosan increases in the sequence, N‐ethyl CS < N‐butyl CS < N‐heptyl CS < N‐lauryl CS. The same results arise from the spin‐lattice relaxation time (T1) for these N‐alkyl chitosan derivatives.