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CHAPTER 9: THE WORLD OF PLASTICS AND POLYMERS
1. Give two examples each of natural and of synthetic polymers.
Examples of natural polymers: Cotton, silk, natural rubber, cellulose, wool, and DNA.
Examples of synthetic polymers: Kevlar, vinyl, nylon, Dacron, polyethylene, polypropylene,
and synthetic rubber.
2. Polymers sometimes are referred to as macromolecules. Explain.
The size and mass of a polymer makes the name macromolecule seem reasonable, because
the prefix macro – means large. Individual polymers may involve thousands of atoms, and
molecular masses can reach over a million grams per mole.
3. Equation 9.1 contains an n on both sides of the equation. The one on the left is a coefficient;
the one on the right is a subscript. Explain.
The n on the left side of the equation gives the number of monomers that react to form the
polymer. Thus, it is a coefficient. The n on the right side is a subscript; it represents the
number of repeating units in the polymer.
4. In equation 9.1, explain the function of the
over the arrow.
represents a free radical that initiates the polymerization.
5. Describe how each of these strategies would be expected to affect the properties of
polyethylene. Also provide an explanation at the molecular level for each effect.
a. increasing the length of the polymer chain
b. aligning the polymer chains with one another
c. increasing the degree of branching in the polymer chain
a. At the molecular level, increasing the length of the polymer chain would increase its molar
mass and the extent of its interactions with neighboring chains. This would be expected to
somewhat increase the polymer’s rigidity, strength, and melting point.
b. At the molecular level, aligning polyethylene chains with one another means that the
structure is more crystalline and highly ordered. This would be expected to give the polymer