Addition polymerisation
Many small monomer molecules join to make one very large
polymer molecule
Addition polymers are made from alkenes : the C=C bond in each
monomer opens and the molecules link into a chain. No other product
forms, so the repeating unit has the same atoms as the monomer
Ethene makes poly(ethene) ; propene makes poly(propene)
To draw it: draw the monomer with its double bond replaced by a single
bond , put brackets round it, extend a bond through each side
of the brackets, and write n n n
To get the monomer from a repeating unit, do the reverse: remove the
brackets and put the double bond back between the two carbons
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Addition polymerisation — making poly(ethene) n C H H C H H n molecules of ethene (the monomer) high pressure and a catalyst C H H C H H n poly(ethene) (the polymer) The C=C double bond opens out and the monomers join end to end. The bonds are drawn passing through the brackets to show the unit repeats. Nothing else is made — this is why it is called addition polymerisation. The formation of poly(ethene): n molecules of ethene with the C=C shown, an arrow, and the repeating unit in square brackets with single C–C bond, bonds extending through the brackets, and n
Three things the repeating unit must have: a single C–C bond, the
bonds extended through the brackets, and every side group
kept in place. Adding extra atoms on the extending bonds contradicts the
structure
The mark scheme ignores the brackets and n n n
The rest of this topic is in the full Exam Guide The complete AQA GCSE Chemistry guide — every topic, exam checklist and common mistake — is coming soon. Until then, the first topic in every unit is free to read.
In the full topic
• Addition polymerisation• Condensation polymerisation [Higher Tier]• Amino acids [Higher Tier]• DNA and other natural polymersRead the free chemistry topics →