Polymer Definition. A polymer is a large molecule made up of chains or rings of linked monomer units. Polymers usually have high melting and boiling points. Examples: PVC (poly vinyl chloride), polystyrene, cellulose.olymer Definition. A polymer is a large molecule made up of chains or rings of linked monomer units. Polymers usually have high melting and boiling points. Examples: PVC (poly vinyl chloride), polystyrene, cellulose.