Addition polymerization of alkenes
3g.
describe the addition polymerization of alkenes and
identify the repeat unit given the monomer, and vice versa
Connector - Draw the major addition products for the
reactions between i) Br2 & ii) HBr with:
propene, but-1-ene, but-2-ene, and 2-methylpropene
Crowe2008
Br Br H
H
C–C
C
H
H
H
H
H
H
Br H
C–C
C
H
H
H
H
Markovnikov addition
H
Br Br H
H
C C C
C
H
H H H
H
H
H Br H
H
C C C
C
H
H
H H H
Markovnikov addition
H Br Br H
H
C C C
H
C
H
H
H H H
C C
H
H
C C C
C
H
Br Br
H
H Br H
H H H
H
CH3
CH3
H
H
Br
C C
H
CH3
CH3
Markovnikov addition
Monomers and Polymers
Ethene is called a MONOMER because
it is just one small molecule. We can
use ethene to make plastics…
Ethene
Step 1: Break the double bond
Step 2: Add
lots of the
molecules
together:
This molecule is called POLYETHENE,
and the process that made it is called
POLYMERISATION
Manufacture of addition polymers.
• An addition reaction is one in which two or more molecules join
together to give a single product. During the polymerisation of
ethene, thousands of ethene molecules join together to make
poly(ethene) - commonly called polythene.
• The number of molecules joining up is very variable, but is in the
region of 2000 to 20000.
Conditions
• Temperature: about 200°C
• Pressure: about 2000 atmospheres
• Initiator: a small amount of oxygen as an impurity
Another way of drawing it…
H
H
C C
H
H H H H H H H H H H
H C C C C C C C C C C
H
H H H H H H H H H H
1
2
3
4
5
And
lots
more..
thousands
This is called addition polymerisation and is written as:
H
n
H
C
C
H
H
ethene
Pressure
high
temperature
catalyst
H H poly(e)thene
C C
H H n
n = a large number
Draw the equations for the polymerisation of the
following alkenes and name the polymer:
n
H
CH3
C
C
H
H
propene
F
n
F
C
C
F
F
tetrafluoroethene
F
F
C
F
C
F
Poly(tetra
or PTFE
H
n
H
H
C C
H
CH
C 3
H
H
H CH3
Poly(propene)
C C
H H
n
propene
F
n
F
C C
F
F
tetrafluoroethene
F F
C C
F F
n
Poly(tetrafluoroethene)
or PTFE
ou may be asked to show polymerisation using three or more monomer units. e.g.
Draw a similar process for propene and chloroethene
Thermosoftening polymers
or thermoplastics:
These soften when heated and can
be remoulded into new shapes
weak
intermolecular
forces –
these let the
chains slide
past each other
What are thermosetting plastics?
Some polymer chains cannot slide past each other.
strong
intermolecular
forces
(cross-links) –
these hold the
chains firmly in
place
Plastics made of these polymers cannot be
stretched, are rigid and have a high melting
point. They are called thermosetting plastics
(or ‘thermosets’).
Homework - Research the problems and
solutions wrst the use of polymers.
You should include the following key areas:
• Energy
• costs
• sources
• Resources used
• Disposal problems
• biodegradable polymers
• Carbon footprint
• Recycling/reusing
Use the above data to compare the properties of PLA with polystyrene
and PVC.
Produce graphs to show the tensile strength, elastic modulus and tear
strength as both hard sheets and soft films.
How does PLA compare with conventional polymers?
Tensile strength
C
PV
e
re
n
How does PLA compare with
conventional polymers?
po
So
f
ly
st
y
tP
LA
C
PV
po
H
ar
d
ly
st
y
P
re
n
e
LA
90
80
70
60
50
40
30
20
10
0
elastic modulus
3
2.5
2
1.5
1
0.5
0
Hard PLA
polystyrene
PVC
Soft PLA
polystyrene
PVC
Soft PLA
polystyrene
PVC
tear strength
900
800
700
600
500
400
300
200
100
0
Hard PLA
polystyrene
PVC
hard sheets
soft films
Life cycle analysis
Life cycle analyses of three different materials for gas pipes
cast iron
polythene
PVC
POCP
216
216
215
ECA
26
6.4
3.9
GWP
31
22
21
AP
13
2.5
1.1
ADP
9.7
1
0.45
HT
14
1.9
0.76
NP
2.5
0.61
0.33
OTL
11
0.39
0.48
ODP
1.25
0.17
0.07
EC
748
303
139
•Present the information in the form of a bar chart so that the
environmental features may be compared.
•Suggest why the scientists may have been surprised by their
findings.
Life cycle analyses of three different
materials for gas pipes
cast iron polythene PVC
•Suggest why the scientists may have
been surprised by their findings.