Effect of total degree of substitution on molecular parameters of cellulose acetate

An attempt was made to establish for cellulose acetate (CA) the relationship between the molecular properties, the total degree of substitution 〈〈F〉〉 and the degree of solvation. For this purpose, the comprehensive solution data for CA with 〈〈F〉〉 = 0.49-2.92 in previous papers were analyzed. In addition, the strength of the solvation was estimated from the chemical shift of O-acetyl- and hydroxyl-protons in NMR spectra and the number of the solvated solvent molecules at infinite dilution (s_o) was determined from the adiabatic compressibility. The strength of solvation and s_o increased with the dielectric constant ? of the solvent. The close correlation between s_o, the unperturbed chain dimension A and the free draining effect was demonstrated; these three quantities and the exponent a in the Mark-Houwink-Sakurada equation attained their maximum at $\text{〈〈F〉〉 ? 2.5}$, if CA is dissolved in dimethylacetamide. The characteristic variation of the chain rigidity, estimated from A, and of the draining effect with ? of the solvent and 〈〈F〉〉 can be reasonably explained by the solvation. The cellulose molecule dissolved in a hypothetical non-polar (? = 1) solvent was shown to be a freely rotating chain, by duplicated extrapolation A for CA to 〈〈F〉〉 = 0 and to ? = 1.