How does a radical start the polymerization of ethylene?

In the context of chemistry, a radical initiates the polymerization of ethylene through a process known as chain-growth polymerization. The process begins with the following steps:1

• Initiator Decomposition: Compounds such as peroxides serve as initiators. These compounds break down to form highly reactive species called radicals, which contain an unpaired electron.12
• Chain Initiation: The initiator radical (designated as R·) reacts with an ethylene monomer (CH₂=CH₂). During this addition, the radical bonds to the monomer, creating a new, larger radical species that possesses an unpaired electron on one of its carbon atoms.1
• Chain Propagation: This newly formed radical then reacts with another ethylene molecule, continuing the process of adding monomers successively to the growing chain.1

This cycle of radical addition continues until the supply of ethylene is depleted or the chain is terminated through reactions such as the combination of two chains or disproportionation. This specific method of free-radical polymerization is typically used to produce low-density polyethylene (LDPE).13