A polymer is a very large molecule in which one or two small units is repeated over and over again. The small repeating units are known as monomers. Imagine that a monomer can be represented by the letter A. Then a polymer made of that monomer would have the structure:
In another kind of polymer, two different monomers might be involved. If the letters A and B represent those monomers, then the polymer could be represented as:
A polymer with two different monomers is known as a copolymer.
The number of monomers (As or Bs) in a polymer is very great indeed. To accurately represent the first polymer above, for example, it might be necessary to write a few hundred or a few thousand As. We would have to fill up a page or two of this book to give an accurate formula for such a polymer.
Polymers are very common in nature; some of the most widespread naturally occurring substances are polymers. Starch and cellulose are examples. Green plants have the ability to take the simple sugar known as glucose and make very long chains containing many glucose units. These long chains are molecules of starch or cellulose. If we assign the symbol G to stand for a glucose molecule, then starch or cellulose can be represented as:
Again, a real molecule of starch or cellulose contains hundreds or thousands of these G units.
Words to Know
Copolymer: Polymers formed from two or more different monomers.
Monomers: Small molecules that join together to form polymers.
Plastics: A group of polymers that are capable of being softened and molded by heat and pressure.
Scientists began to make synthetic polymers long before they really understood the structure of these giant molecules. As early as the 1860s, chemists were exploring ways in which naturally occurring polymers such as cellulose could be modified to make them more useful. These polymers eventually became known as plastics. The term comes from the fact that most early polymers could be melted, bent, and shaped.
The first truly synthetic polymer was invented around 1910 by Belgian-American chemist Leo H. Baekeland (1863–1949). Baekeland reacted phenol with formaldehyde to produce a tough, hard, material that did not dissolve in water or other solvents and that did not conduct an electric current. He named the product Bakelite. Bakelite rapidly became very popular as casing material for a number of household products, such as telephones and electrical appliances.
Credit for first recognizing the chemical nature of polymers is usually given to German chemist Hermann Staudinger (1881–1965). In 1926, Staudinger suggested that polymers are very large molecules consisting of one or two simple units (the monomers) repeated over and over again. He received the Nobel Prize in chemistry in 1953 for this discovery.
In the last half of the twentieth century, chemists invented dozens of different kinds of synthetic polymers. Most of these compounds were developed to have certain special and desirable properties, such as toughness; resistance to wear; low density; resistance to water, acids, bases, and other chemicals; and resistance to the flow of electric current.
[ See also Plastics ]