Question

Question: Draw a stepwise mechanism for the following addition reaction to an alkene.

Short answer

Answer

Polymerization includes two steps

Formation of initiator

Polymerization reaction

Step-by-step solution

Radical polymerization

Radical polymerization includes polymerization reactions initiated by free radicals. One of the most common radical initiator is the peroxy radical.

In these reactions, the initiation step is the formation of a peroxy radical from an organic peroxide which reacts with a monomer unit to produce monomer free radical

The monomer free radical reacts with another monomer unit. This reaction is repeated forming long-chain polymers.

Radical copolymerization

When two different monomers polymerize to form a long chain polymer that contains the monomers in an alternating sequence, it is called copolymerization.

If the copolymerization reaction is initiated by free radicals, it is called a radical copolymerization reaction.

In radical copolymerization, the initiator radical reacts with one of the monomers to form a carbon free radical. This carbon free radical is added to the other monomer.

This addition causes a reversal in the philicity of the radical. Therefore, the polymer will have monomers in an alternating sequence.

 Step 3: Radical copolymerization of ethanol and hexene

In the first step, the O-O bond of the peroxide undergoes homolytic cleavage to form peroxy radicals.

Formation of peroxy radical

The peroxy radical reacts with ethanol to form carbon free radical. This is shown by reaction [1]. This radical reacts with hexene shown by reaction [2]. This causes a reversal in the philicity of the radical.

Due to reversal in philicity, the radical formed from reaction [2] will have an affinity towards ethanal which reaction is shown by [3]. The philicity is further reversed and the radical formed in reaction [3] will have an affinity toward hexene.

Reaction [2] and [3] are repeated in cycles to form long-chain polymers.

Polymerization of ethanal and hexene