Condensation Polymerisation

 
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Students learn to explain what is meant by a condensation polymer and describe the reaction involved when a condensation polymer is formed

In a condensation polymerisation reaction (sometimes called step-growth polymerisation), two monomer molecules react together to form a dimer (two molecules joined together), which can in turn react with other monomer and dimer molecules, etc., until a long polymer is formed.

Two different functional groups are involved in any condensation polymerisation; these may be on two different monomer species (AA and BB) or on the same monomer (AB). Two possible reactions you could use for making poly(ethylene terephthalate) (PET) are given below:


The two reactions involved in the synthesis of PET.

In a condensation polymerisation, where each bond-forming reaction generates a molecule of water. The synthesis of PET, given above, is a condensation polymerisation: an alcohol combines with a carboxylic acid group to give an ester link and water. Another condensation polymerisation is the preparation of nylon-6,6, in which a peptide bond is generated:


The formation of Nylon-6,6.

Let's look at the chemistry of these reactions in a little more detail, and compare this form of polymerisation to addition polymerisation (the type of reaction use to produce poly(ethene) from ethene).