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Ch.12 - Solids and Modern Material
Chapter 12, Problem 70

Saran, the polymer used to make saran wrap, is an addition polymer formed from two monomers—vinylidene chloride and vinyl chloride. Draw the structure of the polymer. (Hint: The monomers alternate.)

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Identify the monomers: Vinylidene chloride is \( \text{CH}_2=\text{CCl}_2 \) and vinyl chloride is \( \text{CH}_2=\text{CHCl} \).
Understand that in an addition polymerization, the double bonds in the monomers open up to form single bonds, linking the monomers together.
Recognize that the polymer is formed by alternating the two monomers, so the repeating unit will consist of one vinylidene chloride and one vinyl chloride.
Draw the repeating unit by connecting the carbon atoms of the monomers in a head-to-tail fashion: \( -\text{CH}_2-\text{CCl}_2-\text{CH}_2-\text{CHCl}- \).
Extend the repeating unit to show the polymer chain, indicating that the pattern continues indefinitely: \( -[\text{CH}_2-\text{CCl}_2-\text{CH}_2-\text{CHCl}]_n- \), where \( n \) represents the number of repeating units.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Addition Polymerization

Addition polymerization is a chemical reaction in which monomers with unsaturated bonds (like double bonds) react to form a polymer. This process involves the breaking of the double bonds in the monomers, allowing them to link together in long chains. The resulting polymer retains the main chain of the original monomers, making it a key method for synthesizing various plastics and synthetic materials.
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Monomer Structure

Monomers are the basic building blocks of polymers, typically small molecules that can join together to form larger structures. In the case of saran wrap, the monomers vinylidene chloride and vinyl chloride each contain a carbon-carbon double bond, which is crucial for the polymerization process. Understanding the structure of these monomers helps in visualizing how they will combine to form the polymer.
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Polymer Structure and Alternation

The structure of a polymer is determined by the arrangement of its monomers. In the case of saran, the hint indicates that the monomers alternate, meaning that the polymer chain will consist of repeating units of vinylidene chloride and vinyl chloride in an alternating pattern. This alternation can affect the physical properties of the polymer, such as its strength and flexibility.
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