In free-radical chain-growth polymerization, chain termination can occur by a disproportionation step in which a hydrogen atom is transferred from one growing chain molecule to another one, which produces two dead (non-growing) chains.
:: Chain—CH–CHX  +  Chain—CH–CHX  →  Chain—CH=CHX  +  Chain—CH–CHX
in which, Chain— represents the already formed polymer chain, and  indicates a reactive free radical.