How do free radicals help make plastics and synthetic rubber?
Free radicals are highly reactive chemical species containing one or more unpaired electrons, which play a fundamental role in the industrial production of plastics and synthetic rubber through a process known as chain-growth polymerization.123
The Role of Free Radicals in Polymerization
The process begins with an initiator, such as a peroxide, which decomposes to form free radicals. These radicals react with monomers—the building blocks of polymers—by adding to them and creating a new reactive site with an unpaired electron. This reactive site then attaches to subsequent monomer molecules in a rapid, successive chain reaction, building long polymer chains.23
Applications in Industry
- Plastics: Free-radical polymerization is used to create common plastics like polyethylene and polyvinyl chloride.3
- Synthetic Rubber: Many synthetic elastomers, such as styrene-butadiene rubber (SBR) and nitrile rubber, are produced using radical polymerization. In emulsion polymerization, water-soluble radical catalysts are used to induce this reaction on an industrial scale.45
Additionally, free radicals can be used for cross-linking or vulcanization, a process that improves the strength and elasticity of rubbery materials by creating stable bonds between polymer molecules.46