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How does chain transfer produce branches in low-density polyethylene?

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Diagram illustrating a homopolymer arrangement using polyvinyl chloride as an example, showing a chain of identical repeating vinyl chloride units with the chemical structure highlighted. — polymer Industrial polymers are synthesized from simple compounds joined together to form long chains. For example, polyvinyl chloride is an industrial homopolymer synthesized from repeating units of vinyl chloride.

In the production of low-density polyethylene (LDPE), branches are formed through a process known as chain transfer or "backbiting."

Because growing polyethylene chains are highly flexible, the radical located at the end of a chain can curl around and abstract a hydrogen atom from a CH₂ group located in the middle of the same chain. This action creates a new radical site at that internal position, from which further chain growth continues, resulting in the branched structure characteristic of LDPE.1

These chain-transfer reactions can occur both intramolecularly (within the same chain) and intermolecularly (between different chains). The presence of these long and short branches prevents the polymer molecules from packing closely together in crystalline arrangements, which is what gives LDPE its signature flexibility compared to the linear, highly crystalline structure of high-density polyethylene (HDPE).123