Animation showing the formation of a long chain of the plastic polyvinyl chloride PVC from two molecules of the monomer chloroethene vinyl chloride. During the polymerisation reaction, the double bond between the two carbon atoms black in each monomer is broken, and single bonds red link the monomer units in a chain. PVC is the third most commonly used plastic, and is used to manufacture pipes, electric cable insulation, signs and clothing. In this animation, chlorine atoms are green and hydrogen white.