13C‐NMR spectral studies on the distribution of substituents in water‐soluble cellulose acetate

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Abstract
The degree of substitution (DS) and distribution of O‐acetyl groups of water‐soluble cellulose acetate (CA) were investigated by 13C‐NMR. For this purpose, three different series of CA samples with low DS were prepared by respective homogeneous reaction, i.e., (1) deacetylation of cellulose triacetate (CTA) in acetic acid—water solution (D‐series), (2) reaction of CTA with hydrazine (H‐series), and (3) acetylation of cellulose with acetic anhydride in a 10% LiCl‐dimethylacetamide solution (A‐series). It was found that (i) water‐soluble CA can be obtained only from D‐series products, (ii) the DS value of water‐soluble CA ranges from 0.5 to 1.1, (iii) the D‐series products exhibit little difference between the relative DS values at C‐2, C‐3 and C‐6 hydroxyl groups, and (iv) the relative DS at C‐6 hydroxyl groups is very high compared to those at C‐2 and C‐3 hydroxyl groups in H‐ and A‐series products. Aqueous solution of water‐soluble CA (D‐series sample) showed no gel—sol transition, even when the temperature was raised to 95°C. X‐ray diffraction observations revealed that the water‐soluble D‐series samples were essentially noncrystalline, but the water‐insoluble A‐series samples were crystalline. It was also found that the relative ease of acetylation is C‐6 > C‐2 > C‐3.

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