Polyamides are prepared in a similar way to polyesters but with amine functional groups replacing the hydroxyl functional groups.
For example, Nylon 6.10 (a polyamine) is prepared as follows
Condensation reactions in organic chemistry are reactions where there is an elimination of a small molecule. If ethanol and ethanoic acid (acetic acid) are reacted in the presence of a small amount of
concentrated sulphuric acid an ester in formed (called ethyl ethanoate or ethyl acetate), Both ethanol and ethanoic acid are monofunctional. This means that they have only one functional group each (-OH and -COOH), We can see that the reaction cannot go any further because there are no further functional groups to react.
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However, if each reacting molecule has two functional groups then the reaction can proceed further, For example, let us consider the reaction between the two monomers hexanedioic acid (adipic acid) and ethane-1 ,2-diol (ethylene glycol),
The two difunctional monomers have reacted together to make what is called a dimer. It can be seen that in this case the product still contains two functional groups, so further reaction with monomer can now take place.
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It can be seen that further reaction can now take place between the trimer and another diacid monomer.
These polymerizations proceed by steps by reaction between pairs of functional groups
eventually producing a polymer. Therefore the molecular weight of a reaction mixture rises steadily during a reaction and long reaction times are required to produce high molecular weights. This is opposite to addition Pymerization were high molecular mass
polymer is formed almost immediately.
When trifunctional groups are reacted with difunctional functional groups then the product is no longer a linear polymer; rather it is a network polymer (often called a resin) For example, the Phenol-Formadehyde thermosetting polymer.
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