How does free-radical polymerization produce polyvinyl chloride?

Free-radical polymerization is a chain-growth process used to manufacture polyvinyl chloride (PVC) by linking thousands of vinyl chloride monomer units. The process involves three primary stages:12

• Initiation: Highly reactive compounds known as free-radical initiators—often peroxides—decompose to form radicals, which are species containing an unpaired electron. These radicals react with the vinyl chloride monomer to open its double bond, creating a new radical site on a carbon atom.132
• Propagation: The radical site on the growing chain adds to successive vinyl chloride monomers. Because the chlorine atom provides both steric crowding and a stabilizing effect on the radical, the initiator adds preferentially to the carbon atom without the chlorine, resulting in a head-to-tail arrangement where chlorine atoms are positioned on alternate carbons.1
• Termination: The chain growth continues until the monomer is depleted or the radical sites are consumed through termination reactions, such as the combination of two growing chains.13

This process can be carried out via bulk, solution, suspension, or emulsion polymerization.4