Natural Polymers: Definition, Types & Examples

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  • 0:01 What is a Polymer?
  • 0:50 Types of Polymers
  • 2:05 What Polymers Occur Naturally?
  • 4:59 Lesson Summary
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Lesson Transcript
Instructor: Roger Harris
Discover the chemistry behind everyday substances like hair and starch by learning about polymers. We explore how polymers form, the chemistry of the reactions, and the three main types of natural polymers and their importance in everyday life.

What is a Polymer?

Have you ever ridden a bicycle or even a motorcycle? An essential part of the bike is the chain, which drives the back wheel. Chains are widely used in machinery and even jewelry, such as a bracelet or necklace. All chains share in common a structure made of links. These links are repeated units with similar or identical structure joined in some way. Think of a long train with many similar cars.

Linked chains are also important in chemistry. A polymer is a chain of repeated units. The word comes from the Greek, polu meaning 'many' and meros meaning 'share.' The units that make up polymers are called monomers. The unit of most natural polymers is typically an 'organic molecule', therefore containing carbon - the stuff you, me and all living things are made of.

Types of Polymers

Polymers form by the process of polymerization, where monomers link together to form the chain, like linking pearls on a string. Polymerization usually occurs only in the presence of a catalyst. The units of polymers can be simple or complex. The length of a polymer chain can be long or short. Chemists recognize two main categories of polymers, addition polymers and condensation polymers.

Addition polymerization happens because of an addition reaction where monomers bond together without losing any atoms. This happens with monomers that have double bonds, typically unsaturated carbon molecules. (A saturated compound only has single bonds.) During the reaction, the double bonds open, allowing the monomers to form a long continuous chain. The chemical industry uses addition polymerization widely for creating synthetic polymers, many of which are not biodegradable.

Condensation polymerization occurs when monomers join together but lose some molecules as by-products. This happens when monomers react that have two functional groups, or a distinct group of atoms within a molecule. The molecule lost is often water, which will condense if conditions are right - hence the name.

What Polymers Occur Naturally?

Most of the structures of living things are comprised of natural polymers. There are three main types. One, polynucleotides, which are chains of nucleotides. Two, polyamides, which are chains of proteins. And three, polysaccharides, which are chains of sugars.

You probably already know at least one naturally-occurring polymer: DNA, or deoxyribonucleic acid. You wouldn't be here without it! The DNA molecule is made of monomers called nucleotides. The monomers are linked by a condensation reaction so that many nucleotides are linked in a chain to make the DNA polymer molecule, which is why it's called a polynucleotide.

The blue circle highlights the phosphodiester bond linking two nucleotides in the

When you cut your nails or comb your hair, you are dealing with another naturally-occurring polymer, keratin. Keratin is among the most abundant proteins in humans. Keratin monomers are amino acids, which form the primary structure of all proteins, a second group of natural polymers.

Proteins are condensation polymers made from amino acid monomers. One amino acid's -NH2 functional group reacts with the -COOH functional group of another amino acid, forming a peptide bond, -CO-NH-. The peptide bond is also called an amide bond, so proteins are also called polyamides.

Formation of a peptide bond, joining two amino acids. Note that this is a condensation reaction, producing water.

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