Radikaalpolümeeriseerumine

Radikaalpolümeeriseerumine is a fundamental polymerization process in chemistry. It involves the formation of long polymer chains from monomers through a series of chain-growth reactions initiated by free radicals. These radicals are highly reactive species with an unpaired electron. The process typically proceeds in three distinct stages: initiation, propagation, and termination.

Initiation begins with the generation of free radicals, usually by the thermal or photochemical decomposition of an initiator molecule. This initiator molecule breaks down to form primary radicals. These primary radicals then react with a monomer molecule, abstracting an atom or adding to the double bond, thereby creating a monomer radical.

In the propagation step, the monomer radical reacts with another monomer molecule, adding to it and extending the growing polymer chain. This process repeats rapidly, adding many monomer units to the chain. The radical center is transferred to the newly added monomer unit, allowing the chain to continue growing.

Termination occurs when the growing polymer radicals are deactivated, stopping the chain growth. This can happen through several mechanisms, most commonly by combination, where two growing radical chains couple together, or by disproportionation, where one radical abstracts an atom from another, forming one saturated and one unsaturated polymer chain. Chain transfer reactions can also occur, leading to the termination of one chain and the initiation of another.

Radikaalpolümeeriseerumine is widely used in the industrial production of many common plastics, such as polyethylene, polypropylene, polystyrene, and polyvinyl chloride. The versatility of radical polymerization allows for the synthesis of polymers with a wide range of molecular weights and properties by controlling factors like initiator concentration, monomer concentration, temperature, and the presence of chain transfer agents.