How do chain-growth polymerization and step-growth polymerization differ?

Chain-growth and step-growth polymerization are two distinct mechanisms used to convert monomers into polymers.1

Chain-Growth Polymerization

Also known as addition polymerization, this process involves the successive addition of monomer molecules onto the reactive ends of a growing polymer chain. It typically requires an initiator to begin the process and is most commonly applied to vinyl monomers containing carbon-carbon double bonds. As the chain grows, it functions similarly to adding links to a chain. Prominent examples include polyethylene and polyvinyl chloride.123

Step-Growth Polymerization

In contrast, step-growth polymerization builds molecular weight in a stepwise fashion through the random combination of monomer molecules that contain reactive functional groups. These reactions often occur between two dissimilar monomers, such as acids and alcohols. Many of these processes are also called condensation reactions because they yield by-products like water or hydrochloric acid, though some step-growth reactions do not produce by-products. Common examples include polyesters, polyurethanes, and polyamides (such as nylon).134