Thermotropic liquid crystalline properties of (hydroxypropyl)cellulose derivatives with butyryl and heptafluorobutyryl substituents

Abstract

(Hydroxypropyl)cellulose (HPC) derivatives with butyryl (Bu) and heptafluorobutyryl (7FBu) substituents were prepared in various proportions of the Bu/7FBu groups and at a fixed total DS (DSBu + DS7FBu) of 3.0. Thermotropic liquid crystallinity of the derivatives (Bu7FBu-HPC) was investigated to specify the effect of the fluoroacylation on the mesophase behavior. Thermal transition data were collected using differential scanning calorimetry and polarized light microscopy. The Bu7FBu-HPC samples formed a chiral nematic phase between their glass transition and isotropization temperatures, Tg and Ti-a, respectively; these transition temperatures rose moderately as the 7FBu proportion increased (Tg = − 44 to − 27 °C and Ti-a = 158–190 °C for DS7FBu = 0.04–1.60). The structural property of the mesophase was examined at 70 °C by circular dichroism and other optical measurements. The chiral nematic pitch (P) sensitively increased with increasing 7FBu proportion, while the supramolecular helical arrangement remained right-handed. Selective light-reflection colors were observed for the samples of DS7FBu = 0.04–0.8, covering an entire spectrum range from violet to red. Temperature dependence of P was also examined for selected samples below Ti-a, and it was found to increase with increasing temperature; however, there was no indication of inversion in the handedness of the helical structure. Wide-angle X-ray diffractometry revealed that the increases of P responding to the increases in DS7FBu and temperature were attributable to the decrease of the twist angle between adjacent thin nematic layers.