Chemistry Reference
In-Depth Information
thermosetting condensation polymers. All these polymers are directly synthesized
by condensation reactions. Other condensation polymers like cellulose (1-11) or
starches can be hydrolyzed to glucose units. Their chemical structure indicates
that their repeating units consist of linked glucose entities that lack the elements
of water. They are also considered to be condensation polymers although they
have not been synthesized yet in the laboratory.
In addition polymers, by contrast, the recurring units have the same structures
as the monomer(s) from which the polymer was formed. Examples are polystyrene
(1-1), polyethylene (1-3), styrene-maleic anhydride copolymers (1-26), and so on.
The difficulty with these definitions is that the same macromolecular structure
can be made by different reaction pathways. This situation occurs particularly
when cyclic and linear monomers can produce the same polymer. Thus, nylon-6
can be made by either of two reactions:
H
2
C
CH
2
CH
2
H
-H
2
O
N
CH
2
C
O
CH
2
C
OH
H
2
C
C=O
H
2
N
x
5
5
O
nylon 6
H
2
C
caprolactam
NH
ε
-aminohexanoic acid
(7-1)
The polyamide made from caprolactam is technically an addition polymer by
the above definition, while the product made from the amino acid would be a
condensation polymer. Actually, only the caprolactam synthesis is used commer-
cially, and the product (polycaprolactam
nylon-6) is called a condensation poly-
mer because all polyamides are so classified.
Similarly, polyethylene can be made from ethylene, dihaloalkanes, or diazo-
methane as follows:
5
free radicals
or
Cr
2
O
3
/Al
2
O
3
BF
3
-N
2
nCH
2
=CH
2
CH
2
CH
2
nCH
2
N
2
n
-NaBr
or
(7-2)
Ticl
3
/AlEt
3
etc.
n
2n
5
Na
Br
CH
2
Br +
5
10
This polymer (which is only made from ethylene in practice) is labeled an addi-
tion polymer.
By convention, polymers whose main chains consist entirely of C
C bonds
are generally classified as addition polymers while those in which hetero atoms
(O, N, S, Si) are present in the polymer backbone are considered to be condensa-
tion polymers. [An exception is polyformaldehyde (1-12), which is an addition
polymer.]
a
