Addition Polymers (DP IB Chemistry): Revision Note
Addition polymers
What is addition polymerisation?
Addition polymerisation is an important reaction of alkenes and forms the basis of the plastic industry
Addition polymerisation involves monomers containing at least one C=C double bond
These monomers join together to form a long-chain polymer
The only product is the polymer
Just like in other alkene addition reactions, the π-bond in each C=C bond breaks and allows monomers to link by forming new C-C single bonds
A polymer is a long-chain molecule that is made up of many repeating units
The small, reactive molecules that react together to form the polymer are called monomers
Examples include:
Poly(ethene) - formed from ethene monomers
Poly(chloroethene) or PVC - formed from chloroethene monomers
Representing addition polymerisation
Addition polymerisation reactions can be shown using:
General formulae
Structural / displayed formulae
Just like any other addition reaction of alkenes, addition polymerisation gives only one product
What is a repeat unit?
A repeat unit is the smallest group of atoms that repeats to form the polymer chain
Repeat units are shown inside square brackets [ ]
In poly(alkenes) such as poly(ethene), the repeat unit is the same as the monomer except the C=C becomes a C–C bond
Worked Example
Identify the monomers present in the given sections of addition polymer molecules:
Answer 1:
The monomer is ethenol (CH(OH)=CH2)
The C=C double bond breaks, forming a repeating unit of CH(OH)-CH2
This gives the polymer poly(ethenol)
Answer 2:
To find the monomer, first the repeating unit should be deduced
Repeating units have only 2 carbons in the addition polymer main chain
The monomer is prop-2-enoic acid
Answer 3:
The repeat unit has two –OH groups on adjacent carbon atoms
The monomer is ethene-1,2-diol (CH(OH)=CH(OH))
This forms the polymer poly(ethene-1,2-diol)
Examiner Tips and Tricks
The structure inside square brackets is the repeat unit – not the monomer
The monomer is the same as the repeat unit, but with C=C bonds instead of C–C bonds
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