Chemguide: Support for CIE A level Chemistry


Learning outcomes 21.1(a) and 21.1(b)

These statements are about condensation polymerisation.

Before you go on, you should find and read the statements in your copy of the syllabus.


General

Condensation polymerisation involves monomers joining together with the loss of a small molecule such as water or HCl.

There are two common cases where this happens. One involves the formation of ester linkages to give polyesters such as Terylene; the other involves the formation of amide linkages to give polyamides such as nylon. Proteins and other polypeptides are also formed by condensation polymerisation of amino acids.


Statement 21.1(a) and 21.1(b)(i)

These are about the formation of polyesters like Terylene.

Read the beginning of the page about polyesters. You do not need to know about their manufacture.

Work out the structure of the polyester by putting it together from the monomers as shown in the diagram with the water molecules being removed.

You should also be aware that you could make polyesters using a molecule containing two -COCl (acyl chloride) groups as one of the monomers. The difference this time would be that you would lose HCl rather than water.

For example, you could make Terylene by:


Yet another way of making a polyester (but not Terylene this time) would be to use a single monomer with a -COOH group at one end and an -OH group at the other. For example:


"R" could be any hydrocarbon group - a chain or a ring. There is no specific mention of this in either the syllabus or the teacher support material, but there was a question which expected you to recognise that a particular polymer structure came from a monomer like this. If you hadn't come across it in advance, you would have to be really good to spot this in an exam.


Statement 21.1(a) and 21.1(b)(ii)

This is about the formation of polyamides and polypeptides. A peptide link is exactly the same as an amide link. Chemists call them amides; biologists and biochemists call them peptides. In both cases, you are forming polymers containing the link -CONH-.

You will find rather more than you need on the page about polyamides.

The only thing that you definitely don't need to worry about on this page is the manufacture of nylon-6,6. The preparation of nylon-6,6 in the lab via the nylon rope trick is just a matter of interest as well. However, although you won't be asked about the experimental details of this, you could be given the structure of two monomers similar to these and asked for the structure of the polymer as a part of statement 21.1(c).

The hydrolysis of polyamides comes up in a later statement in this section.

The uses of the polymers at the bottom of the page is just a matter of interest.

Teacher support material simplifies the starting material for nylon-6, by starting from a chain molecule rather than the cyclic caprolactam. They suggest starting from 6-aminohexanoic acid. Make sure that you can see how the nylon-6 structure is derived from this.

6-aminohexanoic acid: H2NCH2CH2CH2CH2CH2COOH

If you can't do this, then you haven't understood this page. Go back and look again at how water gets eliminated during the formation of nylon-6,6.

Then look at the beginning of the page on protein structure. For now, you don't need to read about the primary, secondary and tertiary structure of proteins. That comes up in statement 21.3(d).


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© Jim Clark 2011 (last modified June 2014)