free-radical interlinking

Free-radical interlinking is a chemical process where highly reactive molecules called free radicals, which possess an unpaired electron, form bonds between polymer chains. This process can occur through various methods, including irradiation with ultraviolet light, electron-beam, or nuclear radiation, or by using unstable additives that decompose to form radicals.1

When a free radical is formed, it can abstract a hydrogen atom from a polymer molecule, leaving behind a reactive carbon atom—the radical. This radical can then couple with another radical on a different polymer chain, creating a stable carbon-carbon bond that links the two molecules together. This interlinking process, also known as cross-linking, is crucial for transforming elastomers into more durable rubbery solids. Even polymers that are fully saturated, like polyethylene, can be interlinked using this free-radical method. While sulfur is a common reagent for vulcanization, free-radical interlinking offers an alternative, particularly for polymers without double bonds.1