Chemistry Reference
In-Depth Information
Champetier and Sekiguchi concluded that the intermediate anions are neutralized first by protons
from the lactams or from the polymer amide groups. The neutral molecules subsequently rearrange
with the openings of the penultimate units [
135
,
136
].
O
O
O
OH
O
O
H
R
R
C
NC
NC
C
NC
NC
O
O
O
H
R
C
NC
NC
They also felt that the acylating strength of the acyllactams is enhanced by coordination of the cations
with the imide carbonyl groups [
135
,
136
]. This is based on an assumption that the incorporations of the
lactam units proceed through additions of lactam anions. Protonations and subsequent rearrangements
follow [
135
,
136
]. This type of chain growth is termed
lactomolytic
propagation [
137
]:
N
N
C
C
C
C
NC
+
N
O
O
O
O
Me
Me
O
C
O
N
C
C
H
NC
O
C
N
C
O
H
N
N
O
O
H
Me
O
C
Me
C
O
O
The mechanism implies that the alkaline cation is fixed to the imide group and that a nucleophilic
attack (that is the rate-determining step) by the lactam anion takes place on the endocyclic carbonyl
group of the imide to give a “carbinolate” anion. Proton exchange takes place between this interme-
diate and a lactam monomer. Intramolecular rearrangement results in ring opening of the unit that is
now in the penultimate position.
In anionic activated polymerization of
-caprolactam chain growth involves both free anions and
ion pairs [
138
]. Quantum-chemical calculations suggest that in the alkali metal lactamate molecule
the negative charge is delocalized between the oxygen and the nitrogen heteroatoms. This led to a
suggestion by Frunze et al [
138
]. that the acts of initiation are formations of activated intermediate
chelate type complexes between the activators and the catalyst molecules [
138
]:
e
R
R
O
O
O
C
C
O
+
C
Me
N
C
N
Me
N
C
C
N
O
O
complex
where Me is a metal like Li, K, Cs, etc.
The carbinol fragment of the resulting complex, shown above, undergoes an intramolecular rear-
rangement. It leads to opening of the heterocyclic ring and to growth of the polymer chain by one unit:
