Chemistry Reference
In-Depth Information
O
O
O
O
R
R
+
n
O
O
n
R
N
N
R
N
N '
R'
n
O
O
O
O
R
+
O
n
R'
O
O
O
O
Si
R
Si
+
n
N
N
O
O
n
N
N
R
Si
Si
n
O
O
O
O
Si
+
2n
O
Si
When silylated diamines are used, trimethylsilyl esters of polyamic acids are formed first and then
desilylated with methanol. Due to increased solubility of silylated aromatic amines, the initial
condensations and formations of polyamic acid trimethylsilyl esters can be done in various solvents,
yielding high molecular weight polymers. The highest molecular weights are obtained in dimethyla-
cetamide at 50
C. Other solvents like tetrahydrofuran and chloroform can be used as well, though
they appear to yield slightly lower molecular weight products [
91
].
The films of the silylated precursors of polyamic acid convert directly by heat treatment
to yellow, transparent, and tough films of aromatic polyimides with the elimination
of trimethylsilanol [
91
]. Other preparations of polyimides include the use of di-half esters of
tetracarboxylic acids [
92
]:
O
O
O
O
HO
OH
R
+
n
n
H
2
N
NH
2
R
N
N
HO
OH
n
O
O
O
O
+
+
2n ROH
2n H
2
O
Polyimides can also be prepared by reactions of diimides with dihalides [
93
]:
O
O
+
H
N
N
H
Cl
Cl
O
O
O
O
N
N
n
O
O
