The basic building block of plastic is a molecule called a “monomer” (meaning “one”). Plastics are made by linking “monomers” together into “polymers”
(“many” monomers).

The process of linking monomers into polymers is called “polymerization.” Check out the Animations section to see how plastic molecules join together.

Picture: This is a monomer of a substance called ethylene. Click on the image to see a 3D version.
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Think of it This Way
You can think of a plastic molecule as a chain of paperclips. Each individual paperclip
represents a monomer. The paperclips are linked to form a chain, which is the polymer.