Synthesis of Hydroxypropyl Derivatives of Chitin and Chitosan and Observation of Phase Behavior of Their Aqueous Solutions

Abstract

Hydroxypropyl (HP) derivatives of chitin and chitosan with different degrees of substitution were synthesized via etherification of the polysaccharides with propylene oxide under various conditions. Molecular structure of the HP derivatives was characterized by ¹H and ¹³C NMR spectroscopy. On the basis of the spectral data, we proposed the equations to determine the molar substitution (MS), degree of pendants (DPs) and degree of substitution (DS) of the HP derivatives obtained. Phase behavior and liquid-crystalline characteristics of aqueous solutions of the derivatives were also examined by light absorption and polarized optical microscopy (POM). Aqueous solutions of highly substituted HP derivatives were phase-separated and became turbid at an elevated temperature. The observed cloud point varied sensitively, depending on the degree of substitution and molecular weight of HP derivatives, concentration of the solutions, and coexistence of inorganic salts. POM observations revealed that the formation of an optically anisotropic monophase prevailed in the concentrated solutions of highly substituted HP derivatives.