Draw a stepwise mechanism for the conversion of acrylonitrile $\left({\mathrm{CH}}_2=\mathrm{CHC}\equiv N\right)$to polyacrylonitrile, $\mathbf{-}{\left[{\mathrm{CH}}_2=\mathrm{CHC}\equiv N\right]}_{\mathbf{n}}$, using butyllithium(BuLi) as the initiator and CO₂ as the electrophile to terminate the chain.

A stepwise reaction constitutes a reaction comprising two or more steps in the mechanism. An example of a stepwise reaction is free-radical polymerization, which includes initiation, propagation, and termination.

Polymerization constitutes a process where small molecules called monomers link to form a network molecule called polymers. The molecules created from the polymerization comprises of linear or branched structure.

The general steps involved in converting acrylonitrile to polyacrylonitrile are initiation, propagation, and termination.

In the first step, the creation of carbanion happens by the nucleophilic addition of butyl lithium.

Initiation step

The second step is propagation in which the carbanion incorporates another monomer.

Propagation step

The third step is termination, where the incorporation of electrophile stops the chain leading to the formation of poly(vinyl acetate).

Termination step