Polymers and life's molecules

Polymers are very large molecules made by joining many small monomers. In addition polymerisation, alkene monomers open their double bonds and join in a chain with no other product: ethene makes poly(ethene), and propene makes poly(propene). In condensation polymerisation, two different monomers, each with two functional groups, join and give off a small molecule such as water each time; polyesters are made this way.

Living things rely on natural polymers. DNA is a polymer of nucleotides. Proteins are polymers of amino acids. Starch and cellulose are polymers of glucose. Many plastics do not biodegrade, so they persist in landfill and oceans. Reusing and recycling plastics, and developing biodegradable polymers, help reduce the problem.