Viscosity‐molecular weight relationships for cellulose acetate

Six fractions have been obtained from a technical cellulose acetate and their molecular weights determined osmotically. Viscosity data are presented for the fractions in acetone, methyl acetate, acetic acid, aniline and pyridine at 25° and values of K and a in the expression [n] = KMa are given. Although logarithmic plots of [n] against M are fairly well represented by straight lines, some scatter is observed and a possible tendency to downward curvature at higher molecular weights. Reasons for scatter and curvature are discussed and it is suggested that a linear relationship between [n] and M may apply at lower molecular weights, the chains being considerably extended. At higher molecular weights some coiling of chains is possible. There seems to be no clearly defined relationship between the values of K and a and the solvent power of the solvent. Values of a for basic solvents are in agreement with predictions based on the ability of such solvents to break‐intramolecular polymer bonds but those for acidic solvents are not.