An explanation of the solubility behaviour of cellulose acetate in various solvents in terms of supermolecular structure formed by introduction of a substituent group into the glucopyranose unit

Abstract

AbstractAn attempt is made to explain the solubility behaviour of cellulose derivatives with hydrophobic substituent groups towards several solvents in terms of supermolecular structure concepts, such as the degree of breakdown in intramolecular hydrogen bonds and conformational variety in the C1—O—C4 glucoside linkage, which depend on the total degree of substitution 〈〈F〈〈 and the distribution of substituent groups in the anhydroglucose (AHG) unit 〈〈fk〈〈 (k = 2, 3, and 6), and solvation.For this purpose, cellulose acetate (CA) samples with a wide range of 〈〈F〈〈 values were synthesized and the dependence of supermolecular structural parameters, including Xam(Ck) (k = 3, 6) (degree of breakdown in intramolecular hydrogen bond at Ck position) and Δ1/2(Ck)(k = 1,6) (half value width of Q. carbon NMR peak), on 〈〈F〈〈 or (〈fk〈〈 was investigated. It has been shown that a considerable breakdown in O3—H—O'5 hydrogen bond or allowance of wide variation in chain conformation around the C1—O—C'4 linkage is a minimum condition necessary for CA to dissolve in solvents, irrespective of type of solvent. Water‐solubility of CA is mainly governed by the supermolecular structure induced by the introduction of substituents at the C3 position and number of residual hydroxyl groups at the C6 position. Acetone‐solubility of CA is mainly governed by solvation of the side chain but an intramolecular interaction between acetyl groups and ring oxygen bonds tends to hinder its solubility at high values of 〈〈F〈〈. DMSO behaves as an amphoteric solvent solvating both hydroxyl and O‐acetyl groups in CA molecules.