EFFECT OF TEMPERATURE ON THE REFLECTIVE PROPERTIES OF CHIRAL NEMATIC (TRITYL) (HEXYL)-CELLULOSE FILMS

6-O-Trityl-2,3-O-hexyl cellulose derivatives form solid films with 'frozen in' chiral nematic order when cast from several organic solvents. Casting from chloroform or tetrahydrofuran can result in films that display iridescent colours due to the chiral nematic reflection band. Films with both left-handed and right-handed chiral nematic structure have been prepared. The chiroptical behaviour of these coloured films has been examined as a function of temperature. The chiroptical activity of the films below the glass transition temperature of the polymer is quite stable, but above this temperature the intensity of the reflection band changes reversibly or irreversibly, depending on the polymer.