Page 353 - Carrahers_Polymer_Chemistry,_Eighth_Edition

316 Carraher’s Polymer Chemistry

3. Starch is composed of two major components—amylopectin and amylose. It is the second
most abundant polysaccharide and found largely within plants.
4. Polyisoprenes form the basis of many natural polymers, including the two most widely known
natural plastics gutta percha and balata and an elastomer known as H. brasiliensis, or NR.
The hard plastics balata and gutta percha are trans isomers while NR is the cis isomer of
1,4-polyisoprene. The polymer chain of amorphous NR and other elastomers uncoils during
stretching and returns to its original low-entropy form when the material is above its T . Chain
g
slippage is minimized through the presence of cross-links. Unlike other solids, stretched rub-
ber contracts when heated. The long-range elasticity is dependent on the absence of strong
intermolecular forces. Eventually, NR formed the basis of the rubber industry through gain-
ing knowledge of such factors as cross-linking that allowed the material to remain coherent
but elastomeric even when exposed to moderate temperatures.
5. Melamines are polymeric agents that play many roles in nature, including forming our skin
pigmentation and with its growth through exposure to sunlight, acting to protect us from the
harmful effects of the sunlight.
6. Lignin is a noncellulosic resinous component of wood. It is the second most abundant renew-
able natural resource. It has alcohol and ether units with many aromatic units. Much of lignin
is sheet like in structure.

GLOSSARY

Accelerator: Catalyst for the vulcanization of rubber.
Alkali cellulose: Cellulose that have been treated with a strong basic solution.
α-Cellulose: Cellulose that is not soluble in 17.5% basic solution.
α Helix: Right-handed helical conformation.
Amylopectin: Highly branched starch polymer with branches or chain extensions on carbon 6
of the anhydroglucose repeating unit.
Amylose: Linear starch polymer.
Antioxidant: Compound that retards polymer degradation.
Balata: Naturally occurring trans-1,4-polyisoprene.
β Arrangement: Pleated sheet-like conformation.
β -Cellulose: Cellulose soluble in 17.5% basic solution but not soluble in 8% caustic solution.
Boeseken-Haworth projections: Planar hexagonal rings used for simplicity instead of stag-
gered chain forms.
Carbohydrate: Organic compound often with an empirical formula CH O; sugars, starch, cel-
2
lulose, are carbohydrates.
Carbon black: Finely divided carbon used for the reinforcement of rubber.
Carboxymethylhydroxyethylcellulose (CMHEC): Made from the reaction of sodium chloro-
acetate and hydroxethylcellulose.
Carrageenin: Mixture of several polysaccharides containing d-galactose units; obtained from
seaweed.
Casein: Milk protein.
Cellobiose: Repeat unit in cellulose.
Cellophane: Sheet of cellulose regenerated by the acidification of an alkaline solution of cel-

lulose xanthate.
Celluloid: Product from a mixture of cellulose nitrate and camphor.
Cellulose: Linear polysaccharide consisting of many anhydroglucose units joined by beta-
acetal linkages.
Cellulose acetate: Product from the acetylation of cellulose.
Cellulose nitrate: Made from the reaction of cellulose and concentrated nitric acid; also known
as gun cotton.

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