How does disproportionation terminate a polyethylene chain reaction?

In the context of free-radical polymerization, the growth of a polyethylene chain is terminated when the reactive radical species at the end of the chain is neutralized.1

Disproportionation is one of the two primary mechanisms for this termination. In this process, a hydrogen atom is transferred from one growing polymer chain to another. This transfer results in the following outcomes for the two chains:1

• The chain that receives the hydrogen atom becomes a saturated alkane molecule.
• The chain that loses the hydrogen atom terminates with a double bond.

By transferring the hydrogen atom, both chains lose their unpaired electrons, thereby ending the chain-growth polymerization process. Alternatively, chains may terminate through a combination reaction, where two growing chains join together to form a single, longer polymer molecule.1