Scientists Say: Polymer

This word describes large molecules made up of smaller chemical building blocks

A polymer called polylactic acid has many uses, from food packaging to medical implants. Polylactic acid is formed from building blocks made of carbon, oxygen and hydrogen molecules (top left and right). That building block, called a monomer, repeats over and over to form a long chain (bottom).

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Polymer (noun, “PAH-leh-mur”)

This word describes large molecules formed from smaller units. Those units are joined by chemical bonds.

Polymers show up everywhere. Plastics are polymers. That includes the hard plastic of water bottles and the plastic fibers that are woven into clothing. Many of these polymers don’t occur in nature. Instead, they are made with chemical reactions in a lab or factory.

Many other polymers occur naturally. These include ones inside our bodies, such as DNA and many proteins. The cell walls of plants contain the polymer cellulose (SELL-you-LOHSE). That polymer is made of molecules of sugar joined together.

The building blocks that make up polymers are called monomers (MAH-nuh-murs). Thousands or even tens of thousands of monomers connect to form a polymer. In some polymers, all the monomers look the same. Other polymers combine several types of monomers. Each has a different arrangement and set of atoms.

Those atoms and the way they are arranged affect a polymer’s properties, such as its hardness or melting temperature. So can the number of monomers. The way monomers are connected matters, too. Lab-made polymers often string together monomers that repeat over and over. The way these units are connected can change the polymer’s structure. Those structures, such as a long chain or something more like a web, give polymers different properties.

In a sentence

With a polymer that conducts electricity, these sunglasses go from light to dark in a flash.

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Carolyn Wilke is a former staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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