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Cellulose derivatives are widely used in biomedical and pharmaceutical applications. Most signi-

cant from a commercial and technical point of view are cellulose ether and cellulose ether esters.

The common structural element of all cellulose derivatives is the polymeric backbone of cellu

lose, which contains as the basic repeating structure a β-d-anhydroglucose unit with three hydroxyl

groups at the C–2, C–3, and C–6 positions available for substitution.

The nature of the substituent and the number of substituted hydroxyl groups are mainly respon

sible for the individual properties of the different cellulose derivatives like solubility, gelation, or

water retention.

Important substituents are low molecular mass alkyl (ethers) and aliphatic or aromatic carboxyl

ate groups (esters), which are listed in Table 27.1.

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The amount of substituent groups on the anhydroglucose unit is usually designated by the degree

of substitution (DS), the average number of substituted hydroxyl groups with a maximum value of

three or by weight percent.

Hydroxyalkyl substituents are characterized by weight percent or by the molar degree of substi

tution (MS), which is the average number of alkylene oxide reacted with each anhydroglucose unit.

The MS includes also side chain formation due to further etheri cation of hydroxyl groups of the

hydroxyalkyl substituent and may take on any value.

Other characteristics of cellulose derivatives that in uence its properties are molecular weight

(MW), MW distribution, and substituent distribution in and over the polymer chains.

The cellulose ether production process is heterogeneous in nature and consists of two major

steps: an initial mercerization step and the nal etheri cation step. Both steps may be conducted

simultaneously or subsequently. In the mercerization step, the cellulose is being suspended and

pre-activated in aqeous caustic soda and then reacted with alkyl chlorides (Williamson etheri ca
tion) and/or epoxides (alkali-catalyzed oxalkylation) as etherifying reagents (etheri cation step).2
Purication is performed by hot water washing or by treatment with mixtures of water and organic
solvents for cellulose ethers without occulation point.
For the synthesis of cellulose ether esters at industrial scale, puried cellulose ether is reacted
with carboxylic anhydrides in acetic acid as solvent system and sodium acetate as catalyst. The
dissolved cellulose ether ester is being obtained then by precipitation after addition of water.
Purication is performed by washing with water.