Question

Explain the difference between the chain and the step growth polymerisation.

Answer 1

Chain growth polymers: Chain growth polymerization is the phrase used to describe the polymers created by adding monomer units one after the other to a developing chain that contains a reactive intermediate (such as a free radical, a carbocation, or a carbanion).

Through a chain reaction process involving specific reactive intermediates, chain growth polymerization occurs. The mechanism entails a sequential process.

1. Initiation: An initiator that can create a reactive intermediate, like a free radical (or a carbocation, or a carbanion), is necessary for chain-growth polymerization. For this, organic peroxides like benzoyl peroxide are typically used. A small quantity of initiator is provided, and it is broken down by heat, light, or an oxidation-reduction reaction to create reactive species, such as free radicals. In order to create a reactive intermediate monomer with an active center, the free radical attacked a monomer molecule.
2. Chain propagation: Now that the monomer has an active center, it attacks other monomer molecules to create dimer, trimer, and so on polymer units with active centers (free radicals).
3. Chain termination: A specific mechanism that involves the removal of the active center from the polymer chain stops its growth.

Step growth polymers: The polymers formed through a series of stepwise condensation reactions involving bifunctional or polyfunctional monomers are called step growth polymers, and the process is termed step growth polymerisation.

The growth step of bifunctional or polyfunctional monomers undergoes polymerization, which entails their progressive condensation with or without the removal of smaller molecules. The process starts with the condensation of two monomer units, which form a dimer, and doesn't require an initiator. The resulting dimer then condenses with the third monomer molecule to create a trimer. The procedure is repeated until a polymer with a very high molecular mass is produced. The method is known as step growth polymerization, and the final polymer is called a step growth polymer since it entails the stepwise creation of a polymer.