Ketjupolymerisaatiossa

Ketjupolymerisaatio, also known as chain-growth polymerization, is a polymerization process where monomers add sequentially to an active site on a growing polymer chain. This process typically involves three distinct stages: initiation, propagation, and termination.

Initiation is the step where an active center is created on a monomer or a small molecule. This active center can be a radical, an anion, or a cation. Once formed, this active center reacts with a monomer, adding it to the growing chain and regenerating the active center at the end of the new chain.

Propagation is the chain-lengthening step. The active center at the end of the growing polymer chain reacts with successive monomer molecules, adding them to the chain. This process continues until the active center is deactivated.

Termination is the step where the active center is destroyed, and chain growth ceases. This can occur through various mechanisms, such as combination (two growing chains joining), disproportionation (hydrogen atom transfer between two growing chains), or chain transfer reactions, where the active center is transferred to another molecule, often a solvent or monomer, leading to the formation of a new, shorter active chain or a terminated chain.

Ketjupolymerisaatiossa is a versatile method used to produce a wide range of polymers, including polyethylene, polypropylene, polystyrene, and polyvinyl chloride. The specific type of active center dictates the mechanism and the resulting polymer structure. For instance, free radical polymerization is widely used for vinyl monomers, while anionic and cationic polymerization are employed for specific monomer types and often lead to polymers with more controlled structures.