Dilute solution properties of water-soluble incompletely substituted cellulose acetate.

Water-soluble incompletely substituted cellulose acetate (CA) was synthesized by the hydrolysis of cellulose diacetate with hydrochloric acid. CA having a degree of substitution DS between 0.39 and 0.81 was water-soluble. The CA (DS=0.49) whole polymer was fractionated into 15 parts, using water–methanol as the solvent–nonsolvent by the successive solution method. The CA(DS=0.49) polymer was soluble in highly polar organic solvents. Solution viscosity, light scattering, and membrane osmometry measurements were performed at 25°C on these fractions in N,N-dimethylacetamide (DMAc), dimethyl sulfoxide (DMSO), water, and formamide. The fractions had ratios of weight-to-number-average molecular weight Mn/Mn of approximately 1.3, independent of Mw. The following relations between limiting viscosity number [η], z-average radius of gyration ‹S2›z1/2 and Mw were obtained: [η]=0.19 Mw0.60 (cm3 g−1) and ‹S2›z1/2=0.50×10−8 Mw0.52 (cm) in DMAc at 25°C. Flory’s viscosity parameter Φ in DMAc was (1.82−2.18)×1023, showing a small molecular weight dependence. The short-range interaction parameter A was estimated thermodynamically as 1.33×10−8 (cm) in DMAc and the conformation parameter σ found to be 2.29. The effect of DS on the molecular characteristics of cellulose acetate is discussed.