Question 25.1: Polypropylene is used in applications that range from indoor...

Polypropylene is used in applications that range from indoor-outdoor carpeting to soda bottles to bank notes^*. It is produced by the addition polymerization of propylene, \text{H}_2\text{C=CH—CH}_3. Draw the structure of polypropylene, showing at least two repeating monomer units, and write its general formula.

Strategy Addition polymers form via a free-radical reaction in which the pi electrons in the carboncarbon double bond of a monomer molecule are used to form carbon-carbon single bonds to other monomer molecules. Draw the structural formula of propylene such that the double bond can be “opened up” to form single bonds between consecutive monomer units.

Setup The structural formula of propylene is

By drawing three adjacent propylene molecules, we can rearrange the bonds to show three repeating units.

^*Student Annotation: An Australian bank note issued in 1988 is printed on polypropylene for increased durability and security.