Types of Polymerization

You are perhaps already aware of various polymers such as PVC, nylon, Bakelite etc. As you will notice although all these are polymers, they have very distinctly different physical appearance and properties. This is due to the difference in their monomers and their polymerization. So let us study a bit more about condensation and addition polymerization.

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Polymerization

By now you are familiar with the concept of polymers. They are huge chains or sometimes even 3D structures of repeating units known as monomers. The monomer is the basic unit of a polymer. These monomers can bond to each other on each side, potentially forever.

So this reaction of combining these monomers to form long chains or three-dimensional networks is known as polymerization. Broadly polymerization can be classified into two categories,

• Step-Growth or Condensation Polymerization
• Chain-Growth or Addition Polymerization

Browse more Topics under Polymers

• Classification of Polymers
• Types of Polymerisation
• Rubber
• Biodegradable Polymers
• Polymers of Commercial Importance
• Condensation Polymerisation or Step Growth Polymerisation

Addition Polymerization

As the name suggests addition polymers form when an addition reaction occurs. The repeating monomers form a linear or branch structure depending on the type of monomer. During addition polymerization, the monomers rearrange themselves to form a new structure. But there is no loss of an atom or a molecule. Again there are four types of addition polymerizations which are

• Free Radical Polymerization: Here the addition polymer forms by addition of atoms with a free electron in its valence shells. These are known as free radicals. They join in a successive chain during free radical polymerization.
• Cationic polymerization: A polymerization where a cation is formed causing a chain reaction. It results in forming a long chain of repeating monomers
• Anionic Vinyl Polymerization: Involves the polymerization of particularly vinyl polymers with a strong electronegative group to form a chain reaction’
• Coordination Polymerization: This method was invented by two scientists Ziegler and Natta who won a Nobel Prize for their work. They developed a catalyst which let us control the free radical polymerization. It produces a polymer which has more density and strength.

Condensation Polymerization

Condensation polymers form from the step growth polymerization. Here when molecules of monomers react to form a bond they replace certain molecules. These molecules are the by-product of the reaction. In most cases, this by-product is a water molecule.

The type of polymers that result from a condensation polymerization depends on the monomers. If the monomer has only one reactive group, the polymers that form have low molecular weight. When monomers have two reactive end groups we get linear polymers. And monomers with higher than two reactive groups results in a polymer with a three-dimensional network.

Polyester and nylon are two common condensation polymers. Even Proteins and Carbohydrates are a result of condensation polymerization.

Addition Polymerization vs. Condensation Polymerization

Let us do a comparative analysis of the two types of polymerization to understand them better.

• In addition polymerization monomers only join at the active site of the chain. But in condensation polymerization, any molecule can react with any other.
• In addition polymerization, there are three distinct steps. Initiation, propagation and finally termination. In condensation polymerization, there is no termination step. The end groups remain reactive through the entire process.
• Addition polymerization results in homo-chain polymers whereas condensation polymerization results in hetro-chain polymers.
• The most significant difference is that in addition polymers there is no loss of atom. But in condensation reaction, there is a loss of a molecule of water, ammonia etc as a by-product.

Solved Question for You

Q: Here, product follows which of the following

1. Free radical substitution mechanism
2. Free radical addition mechanism
3. Electrophilic substitution mechanism
4. None of the above

Ans: The correct answer is “B”. Free radical addition occurs when halide reacts with alkynes in the presence of peroxides. Two anti-Markovnikov additions occur leading to a geminal dihalide product.