Anionic polymerization

Anionic polymerization is a chain-growth process in which negatively charged active chain ends add monomers. Its living forms can grow with little chain termination or transfer.

Carbanion: A species in which a carbon atom bears a negative charge and a lone pair of electrons. Many carbon–carbon anionic polymerizations propagate through a carbanion at the chain end.
Monomer (polymer chemistry): A small molecule that can join other molecules to form a polymer. Anionic chain ends add monomers whose structures permit nucleophilic attack and stabilize the resulting charge.
Living anionic polymerization of styrene: The controlled growth of polystyrene chains from anionic active centers with minimal termination or transfer. It produces narrow molecular-weight distributions and enables sequential block formation.
Cationic polymerization: A chain-growth polymerization in which positively charged chain ends add monomers. It uses electrophilic rather than anionic active chain ends and favors different monomers.
Initiator (chemistry): A substance that generates reactive species to start a chemical chain reaction. Strong nucleophilic initiators create the negatively charged chain ends that begin polymer growth.
Nucleophilic addition: A reaction in which a nucleophile forms a bond to an electron-deficient atom or group. Monomer addition commonly occurs when the anionic chain end acts as a nucleophile.
Styrene-butadiene-styrene: A thermoplastic elastomer made of polystyrene end blocks joined to a polybutadiene midblock. Sequential anionic polymerization can build its distinct hard and rubbery blocks.
Free-radical polymerization: A chain-growth polymerization in which radical chain ends add monomers. Radical growth commonly undergoes termination and transfer, unlike ideal living anionic growth.
Propagation (chemistry): The repeated reaction steps that extend a growing chain in a chain reaction. Each propagation step adds a monomer while transferring the active negative charge to the new chain end.
Conjugated diene: A hydrocarbon containing two carbon–carbon double bonds separated by one single bond. Conjugated dienes such as butadiene support anionic growth and can yield different microstructures.

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