The structure of solutions and films of cellulose acetate

The optical rotatory dispersion of solutions of cellulose acetates with different degrees of acetylation in a series of solvents is studied. Increasing the degree of esterification of the cellulose acetate results in a shift of the optical rotation to more negative values. These changes have been explained on the assumption of various contributions to the optical rotation from hydroxyl and acetate groups. The cellulose acetate solutions studied fall into two groups. Solutions in acetic acid, dimethylformamide, nitromethane, and acetone give anomalous curves, whereas in methylene chloride, chloroform, tetrachlorethane, and dioxane normal curves of rotatory dispersion are produced. Attempts to fit the results by calculations based on a one‐term Drude equation proved all the curves to be more complex. The influence of solute is probably due to specific interaction with hydroxyl and acetate groups and fixing of rotatory isomers of the side groups. A complex pattern of the rotatory dispersion curves is dictated by the contributions from asymmetric carbon atoms associated with hydroxyl and acetate groups having a different rotatory dispersion. Polymer‐solvent interaction affects the film structure. Crystalline films are obtained from cellulose acetate solutions (AcOH = 60.3%) with anomalous dispersion while solutions with a normal dispersion give amorphous firms.