THERMOTROPIC CELLULOSE DERIVATIVES WITH FLEXIBLE SUBSTITUENTS .4. COLUMNAR LIQUID-CRYSTALS FROM ESTER-TYPE DERIVATIVES OF CELLULOSE

Cellulose tri-n-alkanoates, fully substituted ester-type derivatives of cellulose, having acyl groups with n carbon atoms (3 less-than-or-equal-to n less-than-or-equal-to 18), are prepared and their thermal behaviour studied. It is found that samples of cellulose tri-n-alkanoates with n greater-than-or-equal-to 8 form a novel thermotropic mesophase, characterized by a low birefringence and an extremely high viscosity compared with those of cholesteric mesophases of ether-type derivatives. Photomicroscopic, differential scanning calorimetry, and X-ray diffraction studies indicate that the mesophase formed by the cellulose tri-n-alkanoates is of a hexagonal columnar type in which two polymer chains are included in one hexagonal lattice. Two possible packing structures, resembling direct and inverse hexagonal phases of amphiphilic molecular systems, are proposed and discussed in relation to the chemical structure of the polymer.