Chemistry Reference
In-Depth Information
Because the polymer is soluble in dimethylacetamide containing 5% LiCl, fibers can be spun
directly from solution. This polyamide melts at 371
C with degradation. It is fire-resistant. The fibers
are sold under a trade name of Nomex.
Such aromatic polyamides with regular structure were reported to possess better flexibility and
higher temperature resistance [
74
,
75
]. Preparations of
ordered copolyamides
were described as
follows:
-aminobenzamide) is formed first and then reacted with
isophthaloyl chloride by interfacial condensation techniques to yield a product that melts at about
410
C:
N
,
N
-
m
-phenylene-bis(
m
O
O
O
O
H
2
N
NH
2
N
N
Cl
Cl
+
H
H
H
H
O
O
N
N
N
N
n
H
H
O
O
The above condensation, carried out with terephthaloyl chloride, yields a polymer that melts at
450
C. Preparations of many other wholly aromatic polyamides from aromatic diacid chlorides and
aromatic diamines were reported in the literature [
79
,
80
]. In addition, several polymers are
manufactured from both fully and partially substituted (
para
) structures. They carry the trade name
of HT4.
As described in the previous section, direct polycondensation of various nylon salts is possible
under mild conditions in the presence of polyphosphates and organic bases [
84
]. This reaction, useful
in forming aromatic polyamides, takes place also in the presence of thionyl chloride [
84
]:
O
O
H
2
N
NH
2
Cl
Cl
SOCl
+
O
O
N
N
n
H
H
Metal salts, like lithium chloride, significantly enhance reactions of carboxylic acids with amines
promoted by triphenyl phosphite [
82
]. This allows direct polycondensation of dicarboxylic acids with
diamines and self-condensation of
-aminobenzoic acid [
82
]. The presence of a solvent markedly
enhances the reaction with the best results being obtained in
p
N
-methylpyrrolidone. High molecular
N
weight polyamides form. Mixed solvents, like pyridine and
-methylpyrrolidone, can be used to form
polyisophthalamides [
82
]. This combination of solvents, however, yields only low molecular weight
polyterephthalamides. On the other hand, when the reaction is carried out in the presence of
