Studies on chitin-based liquid crystalline polymers - I. Influence of side chain length on the liquid crystalline behavior of acylated chitin

Methanesulfonic acid method was used to prepare five acylated chitins. Except heptanoyl chitin, four of them, i.e. acetyl chitin, propionyl chitin, butyryl chitin and hexanoyl chitin, had high degree of substitution(from 1.5 to 2.0) and exhibited lyotropic liquid crystalline behavior and cholesteric phase. As the length of the side chain increased the critical concentration (W/W) somewhat increased from 0.21 to 0.26 because the chain rigidity dropped. The critical concentration values of all the four derivatives were much higher than that of chitin (0.12) due to the decrease of intramolecular hydrogen bonds. The four acylated chitin can form typical banded texture after being sheared. There minimum concentrations to form banded texture of them were evidently different, varied from 0.25 (for acetyl chitin) to 0.37 (for hexanoyl chitin). These results further indicated that liquid crystallinity decreased while the length of flexible side substituents increased.