Chemistry Reference
In-Depth Information
Cyclic keto imides as well as linear ones can yield active species through acylation of lactam
anions. This results in formations of growth centers and keto amides:
O
O
O
O
C
C
CH
C
N
CH
2
NC
+
H
O
O
O
O
C
CH
C
N
CH
2
C
NC
H
O
O
O
C
O
O
O
C
CH
C
N
CH
2
NC
+
C
NC
H
O
O
N
C
CH
C
CH
2
+
keto amide
O
O
O
C
O
C
CH
C
N
CH
2
NC
+
O
O
H
H
O
C
O
CH
2
C
NC
+
CH
C
N
H
H
keto amide
a
-hydrogen atoms is much greater than that of the monomers or of
polymer amide groups. Any formation of such structures, therefore, decreases the concentration of
lactam anions.
Side reactions give rise to a variety of irregular structures that may be present either in the
backbones, or at the ends of the polymer molecules, or both. Formation of branches in anionic
polymerizations occurs in polymerizations of
The acidity of keto amides with
-caprolactam [
140
,
141
]. This lactam and higher ones
polymerize at temperatures greater than 120
C. Above 120
C the
e
b
-keto-amide units and possibly the
n
-acyl-keto-amide structures are preserved. They may, however, be potential sites for chain splitting
later during polymer processing that takes place at much higher temperatures [
142
].
A new group of catalysts, metal dialkoxyaluminum hydrides, for anionic polymerizations of
lactams, were reported recently [
143
]. A different anionic mechanism of polymerization apparently
takes place. When
-caprolactam is treated with sodium dialkoxyaluminum hydride, a sodium salt of
2(dialkoxyaluminoxy)-1-azacycloheptane forms:
e
H
OR
Na
NC
O
Al
OR
Such compound differs in nucleophilicity from activated monomers. These salts are products of
deprotonation of lactammonomers at the amides followed by reduction of the carbonyl functions. It is
postulated that during lactam polymerizations, after each monomer addition, the active species form
again in two steps [
143
]. In the first one proton exchanges take place:
