Tuning of the pitch height of thermotropic cellulose esters

Butyric esters of (2-hydroxypropyl) cellulose (BuPC) with different degree of substitution(DS) were synthesized via control of the esterification time of butyryl chloride and (2-hydroxypropyl) cellulose. These BuPCs are therm otropic and displayed different colors at ambient temperature due to the fo rmation of a cholesteric structure and the occurrence of a corresponding ch olesteric reflection. The pitch height was found to increase significantly with a decrease of the degree of substitution. Both the glass transition te mperature and the melting temperature are not affected by variation of the DS. The BuPC samples displayed a banded texture or focal-conic texture, res pectively. The X-ray diffraction studies revealed the presence of a layer s tructure. The cl-spacing between two adjacent layers in the cholesteric str ucture displayed no significant dependence on the DS in the range from 2 to 3.