Chemistry Reference
In-Depth Information
O
N
+
n
n
O
N
NO
O
N
O
O
N
N
n
H
H
The molecular weights of the polymers decrease when the ring sizes of the ketone components
increase. Excess diisocyanate yields branched and cross-linked polymers. The enamine units in the
polymers can be hydrolyzed with formic acid to the corresponding ketones [
77
].
A similar reaction was reported from aromatic isocyanates and imidazoles, where 1,4
tetramethylene-
N
0
-di imidazoles were reacted with aromatic polyisocyanates to form thermoset
N
,
polyamides [
45
]:
H
H
N
N
N
N
N
N
+
Ar(NCO)
x
Ar
Ar
N
N
N
N
4
O
4
O
Another route to polyamides is via the Ritter reaction [
78
]:
O
O
NR
N
+
O
O
H
H
H
2
SO
4
HCOOH
NR
N
O
O
n
When aromatic di nitriles are used, high melting polymers with good thermal stability form [
78
].
Direct polycondensation of various dicarboxylic acids with diamines is possible [
81
] under mild
conditions by using a catalytic system of an enol phosphite in the presence of imidazole. One such
enol phosphite is diethyl,1-methyl-3-oxo-1-butenyl phosphite. Polymers with inherent viscosities of
1-0.25 form. Among the organic bases, imidazole is most effective [
84
]. The reaction is applicable to
both aliphatic and aromatic dicarboxylic acids and diamines.
