Anhydroglucose units, polymeric chain

The degree of polymerization (DP) of cellulose (i.e., the number of anhydroglucose units per chain) varies widely (Table 2) and depends on the source of the cellulose, the extent of cell development within that source, and the meAods used for isolation of the cellulose. Cellulose is poly disperse the DPs reported in Table 2 are weight-average degrees of polymerization (DP J that were determined by viscometric methods (assumes DP , - DP J. 

Due to the 3 hydroxyl groups available for oxidation within one anhydroglucose unit and due to the polymeric character of the cellulose a great variety of structural modifications and combinations is possible. As with other types of chemical changes at the cellulose molecule also in this case the oxidation can affect different structural levels differently. Depending on the oxidative stress imposed on the cellulose, the individual hydroxyls within the AGU and within the polymer chain are involved to varying extent and may respond to further treatment and reactions in a specific way. Despite their low concentration in the imol/g range, oxidative functionalities are one of the prime factors to determine macroscopic properties and chemical behavior of cellulosic materials (Fig. 1). 

The size of the cellulose molecule is normally expressed in terms of their degree polymerization (DP), i.e, the number of anhydroglucose units present in a chain. However, the conformational analysis of cellulose indicates that cellobiose (4-0-a-D-glucopyranosyl-a-D-glucopyranose, Fig. 10.2a) is its basic structural unit [10]. The conformation of the repeating unit of cellulose can be explained if we consider the model proposed for the biosynthesis of glucose [11]. 

Several groups have conducted graft copolymerizations on starch or its purified components, amylose and amylopectin. The syntheses are based on attack of the anhydroglucose unit of starch by cerium (+4) ion. The free radical produced from this attack is then immersed in a monomer solution polymerizable by free radical, chain polymerization and a graft copolymer is formed. A typical synthesis procedure (10,16) is as follows. 

FIGURE 11.2 Straight-chain starch molecule, amylose (CAS 9005-82-7). It is made up of glucose units polymerized by dehydration to form ether links. Once incoipoated into the chains, they are called anhydroglucose units. The a-links shown create a polymer that has a chemically similar monomer but is physically and chemically different from cellulose, formed using p-links (see Figure 10.1),... 

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