GCSE OCR Gateway Organic Chemistry C6.2d Addition Polymerisation

GCSE OCR Gateway Organic Chemistry C6.2d Addition Polymerisation

C6.2d To recall the basic principles of addition polymerization by reference to the functional group in the monomer and the repeating units in the polymer

Addition Polymerisation

Polymer means many (poly) molecules (mer) so a polymer is a substance made from many molecules or mono (one) mers (molecule). 

Examples of addition polymers abound.  Here is a list of some addition polymers you may or may not be familiar with:

Polyethene

Polyvinyl chloride

Polystyrene

Polytetrafluoroethene

Polyacrylonitrile

Polyvinylacetate

Polypropylene

Images are all pretty bland since most look like white or grey powders (see below)

Remove the poly prefix from the name and you have the name of the respective monomer that forms the polymer: e.g. styrene is the monomer from which polystyrene is formed.

So the question is how does the monomer form the polymer?

A good example would be how polyvinyl chloride is formed.

I’ve chosen this example because anyone reading this blog who is under 30 will not remember one of the main uses of “vinyl”. 

Back in the day vinyl was the medium on which all music was crafted and recorded.  Black (usually) vinyl records either played at 45rpm (singles) or at 331/3 rpm Long Playing records or LP’s on what were called record players or stereo’s or hi fi’s. (see below)

Each LP disc usually weighed around 180g.  Formed on both sides were the grooves in which the needle (stylus) ran and moved to reproduce the recorded sound of the band on the LP.

LP sound was warm and vital and rich and strong and analogue.  Unlike the sharp, gritty, patchy digital sound from laser read CD.  CD sound was sampled sound, converted into 1’s and 0’s, whereas the LP analogue sound was whole and complete, there was no sampling.

Polyvinylchloride or pvc was the plastic used for the recorded discs.

PVC was formed from the polymerisation of vinyl chloride CH₂=CHCl

n CH₂=CHCl           ⟶          —(CH₂—CHCl)_n—

where n was a large number possibly up to 1000 or thereabouts (it was never exactly the same for each molecule)

Notice how the polymer has formed from the monomer.

One of the two bonds in the double bond in the monomer has broken open (the weaker of the two actually) and that has allowed a bond to form between this monomer and another in which the double bond has opened up e.g.

CH₂=CHCl   +     CH₂=CHCl  +   CH₂=CHCl   ➞   —CH₂—CHCl—CH₂—CHCl—CH₂—CHCl—

The polymerisation can be shown in this way too:

And for the more technically minded among us at this level here is the preparation of the monomer with polymerisation to follow.

In summary if you know the functional group in the double bonded monomer you an work out from it the structure of the polymer.

There are tables of this data on the internet like this: