CIE AS Chemistry (9701) exams from 2022

Revision Notes

3.8.1 Addition Polymerisation

Addition Polymerisation: Polythene & PVC

Addition polymerisation

  • Addition polymerisation is one of the most important addition reactions of alkenes which form the basis of the plastic industry
  • Addition polymerisation is the reaction in which many monomers containing at least one C-C double bond form long chains of polymers as the only product
    • Just like in other addition reactions of alkenes, the π-bond in each C-C bond breaks and then the monomers link together to form 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
  • A polymerisation reaction can be represented by a general formula or by using displayed formulae
    • Eg. poly(ethene) and poly(chloroethene) (also known as PVC) are polymers made up of the ethene and chloroethene monomers respectively and are commonly used in making plastics

Polymerisation General Formula, downloadable AS & A Level Chemistry revision notes

The general formulae of the addition polymerisation of ethene (1) and chloroethene (2)

Polymerisation Displayed Formula, downloadable AS & A Level Chemistry revision notes

The general formulae of the addition polymerisation of ethene (1) and chloroethene (2)

 

  • Just like any other addition reaction of alkenes, addition polymerisation gives only one product

Deducing repeat units

  • A repeat unit is the smallest group of atoms that when connected one after the other make up the polymer chain
    • It is represented by square brackets in the displayed and general formula
  • In poly(alkenes) (such as poly(ethene)) and substituted poly(alkenes) (such as PVC) made of one type of monomer the repeating unit is the same as the monomer except that the C-C double bond is changed to a C-C single bond

  

Polymerisation Repeating Unit, downloadable AS & A Level Chemistry revision notes

The repeating units of poly(ethene) and poly(chloroethene) are similar to their monomer except that the C=C bond has changed into a C-C bond

Worked example: Identifying monomers

Polymerisation Questions Worked example -Identifying monomers, downloadable AS & A Level Chemistry revision notes

Answer 1:
When ethenol (CH(OH)=CH2) is polymerised, the C-C double bond opens to produce a repeating unit of CH(OH)-CH2. This gives the polymer poly(ethenol)

 

Polymerisation Answer 1 Worked example - Identifying monomers, downloadable AS & A Level Chemistry revision notes

Answer 2:
To find the monomer, first the repeating unit should be deduced. Repeating units have only 2 carbons in the polymer main chain

 

Polymerisation Answer 2a Worked example - Identifying monomers, downloadable AS & A Level Chemistry revision notes

 

Since the repeating unit is now found, it can be concluded that the monomer is      prop-2-enoic acid

 

Polymerisation Answer 2b Worked example - Identifying monomers, downloadable AS & A Level Chemistry revision notes

Answer 3: Again, the repeating unit only has 2 carbons in the polymer chain which in this case are two carbon atoms that each contain one OH group

Thus, when ethene-1,2-diol (CH(OH)=CH(OH)) is polymerised, the C-C double bond opens to produce a repeating unit of CH(OH)-CH(OH) which gives the polymer poly(ethene-1,2-diol)

 

Polymerisation Answer 3 Worked example - Identifying monomers, downloadable AS & A Level Chemistry revision notes

Close

Join Save My Exams

Download all our Revision Notes as PDFs

Try a Free Sample of our revision notes as a printable PDF.

Join Now
Go to Top