Polymers are each and everywhere. Just look around you. Your plastic water bottle. The silicone rubber tips on your mobile phone’s earbuds. The nylon and polyester in your jacket or sneakers. The rubber in the tires on the family car. Now take a look in the mirror. Many proteins in your body are polymers, too. Consider keratin (KAIR-uh-tin), the stuff your hair and nails are made from. Even the DNA in your cells is a polymer.
By definition, polymers are large molecules made by bonding (chemically linking) a series of building blocks. The word polymer comes from the Greek words for “many parts.” Each of those parts is scientists call a monomer (which in Greek means “one part”). Think of a polymer as a chain, with each of its links a monomer. Those monomers can be simple — just an atom or two or three — or they might be complicated ring-shaped structures containing a dozen or more atoms.
In an artificial polymer, each of the chain’s links will often be identical to its neighbors. But in proteins, DNA and other natural polymers, links in the chain often differ from their neighbors.
In some cases, polymers form branching networks rather than single chains. Regardless of their shape, the molecules are very big. They are so big, in fact, that scientists classify them as macromolecules. Polymer chains can include hundreds of thousands of atoms — even millions. The longer a polymer chain, the heavier it will be higher. And, in general, longer polymers will give te materials made from them a higher melting and boiling temperature. Also, the longer a polymer chain, the higher its viscosity (or resistance to flow as a liquid). The reason: They have a greater surface area, which makes them want to stick to neighboring molecules.
Wool, cotton and silk are natural polymer-based materials that have been used since ancient times. Cellulose, the main component of wood and paper, also is a natural polymer. Others include the starch molecules made by plants. [Here’s an interesting fact: Both cellulose and starch are made from the same monomer, the sugar glucose. Yet they have very different properties. Starch will dissolve in water and can be digested. But cellulose doesn’t dissolve and can’t be digested by humans. The only difference between these two polymers is how the glucose monomers have been linked together.]
Living things build proteins — a particular type of polymer — from monomers called amino acids. Although scientists have discovered some 500 different amino acids, animals and plants use only 20 of them to construct their proteins. In the lab, chemists have many options as they design and construct polymers. Chemists may build artificial polymers from natural ingredients. Or they can use amino acids to build artificial proteins unlike any made by Mother Nature. More often, chemists create polymers from compounds made in the lab.