Chemistry Reference
In-Depth Information
●
Condensation polymers
In Chapter 14 (p. 226) you studied the different
addition polymers produced from alkenes. Not all
polymers are formed by addition reactions, though.
Some are produced as a result of a different type
of reaction. In 1935 Wallace Carothers discovered
a different sort of plastic when he developed the
thermoplastic, nylon. Nylon is made by reacting two
different chemicals together, unlike poly(ethene)
which is made only from monomer units of ethene.
Poly(ethene), formed by addition polymerisation,
can be represented by:
This is the same amide link as found in proteins
(p. 243). It is often called the
peptide link
. This
type of polymerisation, in which two kinds of
monomer unit react, results in a chain of the type:
-A-B-A-B-A-B-A-B-A-B-
Generally, polyamides have the structure
O
O
O
O
C
C
N
N
C
C
N
N
H
H
H
H
When nylon is made in industry, it forms as a solid
which is melted and forced through small holes
(Figure 15.19). The long filaments cool and solid
nylon fibres are produced which are stretched to
align the polymer molecules and then dried. The
resulting yarn can be woven into fabric to make
shirts, ties, sheets and parachutes or turned into
ropes or racket strings for tennis and badminton
rackets. The annual worldwide production of nylon
is expected to reach 6 million tonnes by 2015.
-A-A-A-A-A-A-A-A-A-A-
where A = monomer.
The starting molecules for nylon are more
complicated than those for poly(ethene) and are
called 1,6-diaminohexane and hexanedioic acid.
1,6-diaminohexane
H
2
N(CH
2
)
6
NH
2
hexanedioic acid
HOOC(CH
2
)
4
COOH
H
2
N(CH
2
)
6
NHOC
(CH
2
)
4
COOH
H
2
O
amide link
The polymer chain is made up from the two starting
molecules arranged alternately (Figure 15.18) as
these molecules react and therefore link up. Each
time a reaction takes place a molecule of water is
lost.
Figure 15.18
A nylon polymer chain is made up from the two molecules
arranged alternately just like the two different coloured poppet beads in
the photo.
Figure 15.19
Nylon fibre is formed by forcing molten plastic through
hundreds of tiny holes.
We can obtain different polymers with different
properties if we carry out condensation
polymerisation reactions between other monomer
molecules. For example, if we react ethane-1,2-diol
with benzene-1,4-dicarboxylic acid, then we produce
a polymer called Terylene.
This sort of reaction is called
condensation
polymerisation
. This differs from addition
polymerisation, where there is only one product.
Because an amide link is formed during the
polymerisation, nylon is known as a
polyamide
.
