We are going to start right at the beginning – before plastic there were polymers – before polymers it was monomers..
A monomer is a molecule that can join with other molecules to form a chain of molecules.
A chain of monomers (or molecules) is called a polymer.
So, a polymer is a chain of repeating monomers or molecules.
A polymer is a large molecule that is made out of many smaller molecules that are joined together by covalent bonds. It may also be called a macromolecule.
Polymers may consist of just one type of monomer or many different monomers. But the pattern must repeat
So a polymer is many monomers or small molecules, joined together in a repeating pattern. The pattern has to repeat a number of times, (a minimum of 500 was one number I read)
Chains of polymers then bond or stick together to form stuff like cellulose, the woody stuff in plants.
Natural polymers are created as part of ongoing biological processes – cotton is part of a plant, wool is grown by sheep and leather is the skin of what ever unfortunate animal.
Synthetic polymers are, as the name suggests, manmade. The key point here is that though the base material may be a natural product such as oil, the polymers derived from it are not. They are not the result of a natural process but have been created artificially.
Monomors have been isolated and then rearranged in new groupings to form new polymers in a precess known as polymerisation. Read more about it here.