Question

13. Discuss addition and condensation polymerization. Be sure to adequately explain each process.

Answer 1

Addition polymerization: It involves linking of monomer units containing double bonds or unsaturation. The double bond of one monomer breaks and links with the neighbouring monomer. This step can keep on repeating to form a long chain of connected monomers to generate something called a polymer. Polymers can contain more than thousands of monomer units. There is no side product obtained in addition polymerization. Addition polymerization can occur through radical, cationic or anionic mehcanism. It is also termed as chain-growth polymerization which means the monomer unit is added repeatedly to the growing polymer chain. Three steps of addition polymerization are :

1)Initiation: This step is usually done with the help of an initiator to generate the reactive free radical, cation or anion which starts the chain growth reaction.

2)Propagation: A monomer unit adds to the chain and each new monomer creates an active site for the attack of the next species and enable further chain growth.

3)Termination: The reactive free radical, cation or anion is neutralized thereby bringing an end to the reaction.

Condensation Polymerization: In this type of polymerization, 2 molecules react with each other to form a larger molecule also generating a side product which is a smaller molecule. This is a Step-growth polymerization reaction. Step-growth polymerization means that the bi-functional or multi-functional monomers first form dimers or trimers which then react to end up forming long chain polymers. Due to this mechanism, a large number of reactions are needed to form high molecular weight polymers. The side products are those that are formed by the combination of atoms that are eliminated from the 2 reacting species. These can be molecules like water or methanol.

The main mechanistic difference between the two is that addition polymerization proceeds through free radical or cationic or anionic pathways whereas the main reactive component in condensation polymerization is the functional group in the starting monomer.