Chemistry Reference
In-Depth Information
Direct polycondensation of a diamine with dicarboxylic acid was carried out in supercritical
carbon dioxide in preparation of nylon 4,6 [
84
].
H
O
+
H
2
N
N
HOOC
NH
2
N
COOH
n
H
O
This nylon was reported to melt at 210
C.
7.3.4 Aromatic Polyamides
In this section are discussed not only wholly aromatic polyamides, but also some mixed polyamides
prepared from aromatic diacids and aliphatic diamines or vice versa. One such material was already
described in Sect.
7.3.2
. Another one, called Nylon 6T, is formed by interfacial polymerization of
terephthaloyl chloride and hexamethylene diamine:
O
H
N
N
n
O
H
The polymer has good heat stability and the strength is unaffected by heating up to 185
C for 5 h.
The polyamide melts at 370
C. When hexamethylene diamine is replaced with tetramethylene
diamine, the melting point rises to 430
C. The condensation product from isophthalic acid and
tetramethylene diamine melts at 250
C.
Fully aromatic polyamides form from reactions of aromatic diacid chlorides and aromatic
diamines [
79
,
80
]. An example is formation of poly(
m
-phenylene diamine isophthalamide):
O
N
N
n
H
H
O
The polymer can be prepared in dimethylacetamide from isophthaloyl chloride and
m
-phenylene
diamine in the presence of an acid scavenger at room temperature:
O
O
H
2
N
NH
2
Cl
Cl
+
polymer
