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:
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