Radikalpolymerisationer

Radikalpolymerisationer, or radical polymerization, is a chain-growth polymerization mechanism that involves free radicals as the chain-carrying species. This process is widely used for the synthesis of various polymers, including polyethylene, polypropylene, polystyrene, and polyvinyl chloride. The polymerization is initiated by a species that can generate free radicals, typically through the homolytic cleavage of a weak bond. Common initiators include peroxides and azo compounds, which decompose upon heating or irradiation.

Once a radical initiator is formed, it reacts with a monomer molecule, adding to the double bond and creating a new radical on the monomer. This monomer radical then propagates by adding to successive monomer molecules, extending the polymer chain. The propagation step is generally very fast. Chain transfer is an important side reaction that can occur during radical polymerization. This process involves the transfer of a radical from a growing polymer chain to another molecule, such as a monomer, solvent, or even another polymer chain, resulting in termination of the original chain and the formation of a new radical.

Termination of the growing chains can occur through several mechanisms. The most common are combination, where two growing radical chains join together to form a single, longer polymer molecule, and disproportionation, where a hydrogen atom is transferred from one radical chain to another, resulting in two terminated polymer chains, one with a double bond at its end and the other saturated. In some cases, inhibitors can be added to the reaction mixture to scavenge radicals and prevent polymerization. Radical polymerization can be carried out in various phases, including bulk, solution, suspension, and emulsion. Each method has its advantages and disadvantages regarding heat dissipation, molecular weight control, and polymer properties.