ヒドロキシプロピルセルロースのアダマントイル誘導体が濃厚水溶液中で形成するコレステリック液晶構造とその光学特性

抄録

Liquid crystallinity of (hydroxypropyl)cellulose (HPC) derivative in aqueous solution was examined to develop eco-friendly liquid-crystalline system. Bulky adamantoyl group (adamantyl ester) was introduced as a substituent on HPC, and the effects of the degree of adamantoyl substitution (DS_Ad), polymer concentration, and temperature on the chiroptical properties, especially coloration and turbidity, of the aqueous lyotropics were investigated by circular dichroism, CD, and ultraviolet–visible–near-infrared, UV–Vis–NIR, spectrophotometry. Adamantates of HPC (Ad- HPCs) with extremely low DS_Ad (< 0.1) were successfully synthesized by acylation of HPC with 1-adamantanecarbonyl chloride in tetrahydrofuran. Ad-HPCs of DS_Ad ≤ 0.08 were highly soluble in water, and the concentrated aqueous solutions formed a right-handed cholesteric liquid-crystalline phase to impart vivid reflective colorations. The cholesteric helical pitch P, comparable to the wavelength of maximal reflectance λ_max, increased with increasing DS_Ad of Ad-HPC and with decreasing polymer concentration. Wide-angle X-ray diffractometry, WAXD, revealed that the increases of P were attributable to the decrease of the twist angle ϕ between adjacent thin nematic layers. The aqueous Ad-HPC lyotropics were phase-separated and became turbid at an elevated temperature of > ∼30°C. Such a lower critical solution temperature (LCST)-type phase separation behavior of the Ad-HPC/water system was also affected by the hydrophobic adamantoyl group; the observed cloud point T_c was shifted to lower temperature side with increase in DS_Ad, presumably due to the heightening of hydrophobic interactions between the solute Ad-HPCs in water.