Book Cover Chemistry 8th Edition / Chang
Student Study Guide

Chapter 25: Synthetic and Natural Organic Polymers


Index | 25.1 25.2 | 25.3 | 25.4 |

SYNTHETIC ORGANIC POLYMERS (25.1 25.2)

STUDY OBJECTIVES

  1. Define monomer and give several examples of addition polymers.
  2. Define copolymer and give several examples of condensation polymers.
  3. Describe the steps in the addition polymerization process.

Polymers. The word polymer means "many parts." A polymer is a compound with an unusually high molecular mass, consisting of a large number of small molecular units that are linked together. The small unit that is repeated many times is called a monomer. A typical polymer molecule contains a chain of monomers several thousand units long. Polymers are often called macromolecules.

Proteins, nucleic acids, carbohydrates, and rubber are natural polymers. Synthetic polymers such as nylon, polyester, and polyethylene are organic compounds.

Addition Polymers. Addition polymers are made by adding monomer to monomer until a long chain is produced. Ethylene and its derivatives are excellent monomers for addition polymers. In an addition reaction, the polymerization process is initiated by a radical. When ethylene is heated to 250C under high pressure (10003000 atm) in the presence of a little oxygen or benzoyl peroxide (the initiator), addition polymers with molecular masses of about 30,000 amu are obtained. This reaction is represented by:

The general equation for addition polymerization is:

Polyethylene is an example of a homopolymer, which is a polymer made up of only one type of monomer. Substitution of one or more hydrogen atoms in ethylene with Cl atoms, phenyl groups, acetate, cyano groups, and F atoms provides a wide selection of monomers from which to make various homopolymers. For example, substitution of a Cl atom for an H atom in ethylene gives the monomer called vinyl chloride, CH2CHCl. Polymerization of vinyl chloride yields the polymer, polyvinyl chloride.

visual aid Table 25.1 in the text gives the names, structures, and uses of a number of monomers and addition polymers.


EXAMPLE Monomers and Polymers

Write the formulas of the monomers used to prepare the following polymers:

a. Teflon       b. Polystyrene       c. PVC


Addition Polymerization. The addition polymerization process occurs by several steps which are summarized below. The first step is called initiation. This is followed by a chain growth process, and finally a termination reaction.

click on links

1.

2.

3.

Condensation Polymers. Copolymers are polymers that contain two or more different monomers. When monomers A and B are linked by condensation reactions a uniform copolymer, ABABAB can be formed. Nylon and polyesters, such as the well-known Dacron, are copolymers.

Polyester is made by an esterification reaction. When one monomer is an alcohol and the other is a carboxylic acid, they can be joined by an esterification reaction. The alcohol and the acid both must contain two functional groups. The monomers in polyester are the dicarboxylic acid called phthalic acid, and the dialcohol, ethylene glycol.

Condensation reactions differ from addition reactions in that the former always result in the formation of a small molecule such as water. Polyesters are produced from the esterification reaction between an alcohol and an acid. When phthalic acid and ethylene glycol react to form an ester, the first products are:

This molecule can react further from both ends. When this product reacts with another molecule of the diacid, the polymer chain grows longer.

The general formula for this polyester is:


OBJECTIVE CHECK

Complete the following questions to check your understanding of the material. Select the check button to see if you answered correctly.

  1. List three steps occurring during addition polymerization.
  2. What monomer is used to make Teflon ( CF2CF2 )n ?
  3. Is Teflon a homopolymer or a copolymer?


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