|Chemistry 8th Edition / Chang|
|Student Study Guide
SYNTHETIC ORGANIC POLYMERS (25.1 – 25.2)
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 250°C under high pressure (1000–3000 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.
Table 25.1 in the text gives the names, structures, and uses of a number of monomers and addition polymers.
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