Thermotropic Cellulose Derivatives with Flexible Substituents. I. Preparation of Tri-o-(β-methoxyethoxy)ethyl Cellulose and its Cholesteric Mesophase Properties

Tri-o-(β-methoxyethoxy)ethyl cellulose was prepared by reacting the regenerated cellulose with 2-(2-methoxyethoxy)ethyl iodide and characterized as a fully substituted derivative. The resultant derivative forms a thermotropic liquid crystal in the wide temperature range from room temperature to the isotropization temperature of 180°C, showing that the (methoxyethoxy)ethyl side-chain substituent is long and flexible enough to inhibit crystallization of the extended cellulose chains and facilitate formation of liquid crystals. This is the first example of a thermotropic liquid crystalline cellulose derivative with a homogeneous side chain. This type of liquid crystal is cholesteric with a right-handed helical structure. The cholesteric pitch increases with increasing temperature, with the magnitudes comparable to the wavelength of visible light in the temperature range below 120°C.