Skip to content
Dabour HubLEARN · PRACTICE · EXPLORESign inStudent

2.5.12Chemical Bonding, Application Of Chemical Reactions and Organic Chemistry

Addition Polymerisation

5 min read 7 parts Lesson 52 of 54 2 quizzes

0%read

Section 1 of 7Monomers and polymers

Monomers- Polymers - Bonds
Monomer
  • Monomer A monomer is a small, reactive molecule containing a carbon-carbon double bond, C=C.
    • Alkenes are the usual monomers.
Polymer
  • Polymer A polymer is a very long molecule made of thousands of monomer units joined end to end.
Why they join
  • Why they join The reactivity comes from the double bond.
    • One of the two bonds in each C=C breaks open, and each carbon can then bond to a neighbouring monomer.
The product
  • The product Only single bonds remain, so a polymer made from an alkene is saturated and usually unreactive.

Section 2 of 7What happens during the reaction

link reaction
1Double bond opens
  • Double bond opens One bond of each C=C breaks, leaving each carbon with a free bond.
2Monomers link
  • Monomers link The free bonds join to the next monomer's carbons, forming a C−C single bond between units.
3Chain grows
  • Chain grows This repeats thousands of times to build a long chain.
4No other product
  • No other product Nothing is lost, so the polymer is the only product;
    • this is why the process is called addition.

Section 3 of 7Common addition polymers

ethene chloroethene polymerisation
ethene chloroethene polymerisation
ethene bromine addition bromonium
ethene bromine addition bromonium
MonomerPolymer
ethenepoly(ethene), usually called polythene
propenepoly(propene)
chloroethene (vinyl chloride)poly(chloroethene), also called PVC
tetrafluoroethenepoly(tetrafluoroethene), also called PTFE

Section 4 of 7Writing an equation

1
Draw the monomer's structural formula with the C=C shown, and put a lower-case n in front of it to show that many molecules react.
2
Write an arrow, then draw the same atoms as the repeat unit, but with a single C−C bond between the two carbons.
3
Put large brackets around the repeat unit.
4
Extend one single bond from each carbon through the bracket; these are the continuation bonds.
5
Write a small n after the closing bracket to show the unit is repeated n times.

Section 5 of 7Naming and examples

Poly(...)
Naming rule
  • Naming rule Put the monomer's name in brackets after the prefix poly-.
    • The one exception is poly(ethene), which is usually called polythene.
Ethene
  • Ethene n CH2=CH2 → (−CH2−CH2−)n
Propene
  • Propene n CH3−CH=CH2 → (−CH(CH3)−CH2−)n, with a methyl group on every other carbon.
Check yourself
  • Check yourself Know the structural formulae of ethene, propene, chloroethene and tetrafluoroethene, and be able to show each reacting as n molecules.

Section 6 of 7Key terms

TermMeaning
MonomerA small molecule, with a C=C bond, that can join with many others to form a polymer.
PolymerA long molecule made from many repeating monomer units.
Addition polymerisationA reaction in which many alkene monomers join together without any other product.
Repeat unitThe section of a polymer chain that is repeated along its length.
Continuation bondsThe bonds drawn through the brackets showing the chain carries on in both directions.

Section 7 of 7Exam technique

1
Leaving the double bond in the polymer. The polymer contains only single bonds.
2
Forgetting the continuation bonds through the brackets, or the n outside them.
3
Writing the product as a small molecule. The polymer repeat unit has the same atoms as the monomer, just rearranged.
4
Naming the polymer after the wrong molecule; poly(propene) comes from propene, not propane.
\n