Cholesteric properties of cellulose acetate and triacetate in trifluoroacetic acid

• Published in: Macromolecules Vol. 21; no. 10; pp. 2914 - 2917
• Main Authors: Ritcey, Anna M, Holme, Kevin R, Gray, Derek G
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 01-10-1988
• Subjects: Applied sciences; Cellulose and derivatives; Exact sciences and technology; Natural polymers; Physicochemistry of polymers; Infrared spectrometry; Chemical modification; Fourier transformation; Cholesteric state; Optical properties; Concentration effect; Cellulose triacetate; NMR spectrometry; Helical structure; Cellulose acetate; Liquid crystals
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma00188a003

The optical properties of cellulose acetate and cellulose triacetate cholesteric liquid crystals in trifluoroacetic acid are investigated by circular reflectivity measurements. The reflection properties of the cellulose acetate mesophase are extremely time dependent. The observed changes are attributed to trifluoroacetylation of the unsubstituted hydroxyl groups of the polymer. Analysis of the polymer recovered from trifluoroacetic acid solution, by NMR and FT-IR spectroscopy, confirms this chemical modification. No significant decrease in molecular weight occurs on the time scale of the change in optical properties. The presence of trifluoroacetate groups on the cellulose chains causes a reversal of the handedness of the cholesteric supramolecular helicoidal structure and also influences the magnitude of the concentration dependence of the pitch. 15 ref.--AA