Molecular structure and liquid-crystalline characteristics of chitosan phenylcarbamate

Chitosan phenylcarbamate (CtsPC) samples were synthesized to have different degrees of substitution (DS) ranging from approximately 2.7 to approximately 3.7, and the lyotropic liquid crystallinity was mainly characterized by spectrophotometry. The products of DS>2.8 formed a cholesteric type of mesophase in concentrated solutions of >44 wt % with polar aprotic solvents such as N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), and dimethyl sulfoxide (DMSO), and some of the solutions imparted vivid colorations because of selective visible light reflection. The cholesteric helical pitch increased with increasing temperature and with decreasing polymer concentration, but the helical sense remained left-handed under the adopted measurement conditions. It was also found that the helical pitch increased in proportion to the increment of DS, whereas an average degree of phenylcarbamoyl polyaddition in the side chains (DPs) rather affected the pitch distribution measuring an orderliness in the cholesteric structure. With a small increase in DPs (e.g., from 1.01 to 1.04), the cholesteric orderliness decreased and the temperature sensitivity of the pitch turned sluggish. Wide-angle X-ray diffractometry was also used for evaluating the distance and azimuth difference between adjacent nematic thin layers in the cholesteric mesophase.