Main Difference – Addition Polymerisation vs Condensation Polymerisation

Polymerisation is the process of joining a large number of small molecules to make very large molecules. Monomers are the building blocks of polymers. Based on the nature of the chemical reaction involved in the formation of a polymer, there are two types of polymerisation reactions: addition polymerisation and condensation polymerisation. Addition polymerisation produces addition polymers through the addition of olefinic monomers without the formation of any by-product.

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In contrast, condensation polymerisation produces condensation polymers through the intermolecular condensation of two different monomers with the formation of small molecules such as HCl, water, ammonia, etc., as by-products. This is the main difference between addition polymerisation and condensation polymerisation. In addition to this main difference, there are many more differences between these two polymerisation reactions.

This article discusses,

1. What is Addition Polymerisation? – Process, Features, Type of Polymers Produced, Examples

2. What is Condensation Polymerisation? – Process, Features, Type of Polymers Produced, Examples

3. What is the difference Between Addition Polymerisation and Condensation Polymerisation?

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What is Addition Polymerisation

Addition polymerisation is the addition of one monomer to another monomer to form long chain polymers. This process does not produce any by-products. Hence, the molecular weight of the polymer will be an integral multiple of monomer’s molecular weight. The monomers involved in these reactions must be unsaturated (double or triple bonds must be present). During the reaction, unsaturated bonds open up and form covalent bonds with adjacent monomer molecules to form long chain polymers. There are three types of mechanisms in addition polymerisation, namely; free-radical mechanism, ionic mechanism, co-ordination mechanism. Polymers produced by the addition polymerisation process are called addition polymers. Examples of addition polymers include polyvinyl chloride or PVC, poly(propylene), poly(tetrafluoroethene) or TEFLON, etc.


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Formation of PVC


What is Condensation Polymerisation

Condensation polymerisation is the process of intermolecular condensation of two different monomers to form a large chain of polymer molecules. In this process, linking of every two monomer molecules will result in a simple molecule such as HCl, ammonia, water, etc., as a by-product. Hence, the molecular weight of the polymer will be the product of the degree of polymerisation and the molecular weight of the repeating unit. The polymers resulted due to condensation polymerisation are called condensation polymers. Bakelite, nylon and polyester are some common examples of condensation polymers.


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The reaction of 1,4-phenyl-diamine (para-phenylenediamine) and terephthaloyl chloride to produce Aramid


Difference Between Addition Polymerisation and Condensation Polymerisation

Nature of the Monomer

Addition polymerisation: Monomer must have at least a double or triple bond.

Condensation polymerisation: Monomer must have at least two similar or different functional groups.

Nature of Polymer Formation

Addition polymerisation: Addition of monomer results in a polymer.

Condensation polymerisation: Monomers condense to give a polymer.

By-products

Addition polymerisation: This polymerisation doesn’t produce any by-products.

Condensation polymerisation: This polymerisation results in by-products such as water, HCl, CH3OH, NH3, etc.

Molecular Weight

Addition polymerisation: Molecular weight of the resulting polymer is an integral multiple of monomer’s molecular weight.

Condensation polymerisation: Molecular weight of the resulting polymer is not an integral multiple of monomer’s molecular weight.

Size of Resulting Polymers

Addition polymerisation: The reaction results in high molecular weight polymers at once.

Condensation polymerisation: The molecular weight of the polymer increases steadily with the reaction.

Reaction Time

Addition polymerisation: Longer reaction time results in higher yields, but has a minute effect on the molecular weight of the polymer.

Condensation polymerisation: Longer reaction times are crucial to obtain higher molecular weight of polymers.

Nature of the Polymers Produced

Addition polymerisation: Addition polymerisation produces thermoplastics.

Condensation polymerisation: Condensation polymerisation produces thermosets.

Polymer Chain

Addition polymerisation: Addition polymerisation results in homo-chain polymers.

Condensation polymerisation: Condensation polymerisation results in hetero-chain polymers.

Examples of Common Polymers

Addition polymerisation: Polyethylene, PVC, etc.

Condensation polymerisation: Bakelite, nylon, polyester, etc.

Catalysts

Addition polymerisation: Radical initiators, Lewis acid or bases are catalysts in this process.

Condensation polymerisation: Mineral acids and bases are catalysts in this process.

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References:


Gopalan, R., Venkappayya, D., & Nagarajan, S. (2010). Textbook of engineering chemistry (4th ed.). New Delhi: Vikas Publishing House Pvt.