Anionipolymerisation

Anionipolymerisation is a type of chain-growth polymerisation where the active center of the propagating chain is an anion. This process typically involves an initiator that generates an anionic species, which then attacks a monomer. The monomer, having an electron-deficient double bond, readily reacts with the nucleophilic anion, forming a new, larger anion. This newly formed anion is the active center, and it continues to propagate by adding more monomer units.

Common monomers for anionic polymerisation include those with electron-withdrawing groups adjacent to the double bond, such as styrenes, acrylates, methacrylates, and dienes. Initiators can be strong bases like alkali metal alkoxides, organometallic compounds (e.g., alkyllithiums), or even alkali metals themselves. The reaction is often carried out in aprotic solvents to prevent protonation of the anionic active centers.

A key characteristic of anionic polymerisation is its ability to proceed in a living manner under appropriate conditions. Living anionic polymerisation occurs when termination and chain transfer reactions are suppressed. This allows for precise control over molecular weight, narrow molecular weight distributions (low polydispersity), and the synthesis of block copolymers by sequential addition of different monomers. The absence of termination means that the active centers remain alive and can initiate further polymerisation, even after the initial monomer is consumed. This control makes anionic polymerisation a valuable technique for producing specialty polymers with tailored properties.