Page 329 - Carrahers_Polymer_Chemistry,_Eighth_Edition

292 Carraher’s Polymer Chemistry

O
/ \
Cellulose − OH, NaOH + H C − CH 2 Cellulose − ( − O − CH CH −) − CH CH 3 (9.15)
2
2
2
2
Ethylhydroxyethylcellulose
Uses for the water-soluble EHEC include water-borne paints, pastes, polymer dispersions, ceram-
ics and cosmetics, and pharmaceuticals. Uses for organic soluble EHEC include inks, lacquers, and
as coatings.
Cellulose undergoes reaction with activated ethylenic compounds such as acrylonitrile, giving
cyanoethylcellulose via a Michael addition.

Cellulose–OH + H C=CHCN → Cellulose–O–CH –CH –CN (9.16)
2
2
2
9.6 STARCH
While cellulose is the major structural polysaccharide, plant energy storage and regulation utilizes
a combination of similar polysaccharides that combined are referred to as starch. Starch can be
divided into two general structures, largely linear amylase (9.17) and branched amylopectin (9.18).
OH OH OH OH

H O H O H O H O R
H H H H H H H
OH H OH OH OH (9.17)
R H O H O H O H
H OH H OH H OH H OH
Linear amylose

Most starches contain about 10%–20% amylose and 80%–90% amylopectin thought the ratio
can vary greatly. While cellulose can be considered a highly regular polymer of d-glucose with
units linked through a β-1,4 linkage, amylose is a linear polysaccharide with glucose units linked
in an α-1,4-fashion while amylopectin contains glucose units with chains of α -1,4 glucopyranosyl
units but with branching occurring every 20–30 units, with the chain-branch occurring from the 6
position. While this difference in orientation is how the glucose units are connected appears small,
it causes great differences in the physical and biological properties of cellulose and starch. As noted
before, people contain enzymes that degrade the α-glucose units but we are unable to digest β units.
Thus, starch is a food source for us, but cellulose is not. Also, the individual units of cellulose can
exist in the chair conformation with all of the substituents equatorial, yet amylose must either have
the glycosyl substituent at the 1 position in an axial orientation or exist in a nonchair conformation.
OH
OH OH
H O
H
OH H H O H O
R H H H H H
OH OH
H OH O H R H
H OH H OH
OH OH O O
(9.18)
H O H O H O H O R
H H H H H
OH H OH H OH OH H
R H O H O H O H
H OH H OH H OH H OH
Branched amylopectin

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