Anioonpolümerisatsioonid

Anioonpolümerisatsioonid is a type of chain-growth polymerization where the propagating chain end carries a negative charge, typically an anion. This process is initiated by anionic initiators, which are strong bases or nucleophiles. Common initiators include organometallic compounds like alkyllithiums, alkali metal amides, and carbanions. The initiation step involves the attack of the initiator on a monomer, creating a carbanionic species. This carbanionic center then attacks another monomer molecule, propagating the polymer chain. The process continues until termination occurs, which can happen through reaction with impurities, deliberate quenching agents, or by chain transfer reactions.

Anionic polymerization is particularly effective for polymerizing monomers with electron-withdrawing groups attached to the double bond, such as vinyl monomers and dienes. Examples include styrene, butadiene, isoprene, and acrylates. A key advantage of anionic polymerization is its ability to achieve living polymerization under carefully controlled conditions. In living polymerization, there is no spontaneous termination or chain transfer, allowing for precise control over the molecular weight, molecular weight distribution, and polymer architecture. This control enables the synthesis of block copolymers and polymers with specific end-group functionalities. However, anionic polymerization is highly sensitive to impurities like water and oxygen, which can act as terminating agents, requiring strict anhydrous and inert reaction conditions. The polymerization can be carried out in various solvents, including hydrocarbons and polar aprotic solvents, with the choice influencing the polymerization rate and the properties of the resulting polymer.