Chemistry Reference
In-Depth Information
-caprolactone polymerization can be carried with bis(acryloxy-)
lanthanide (II) complexes based on samarium [
110
]. Thus, (ArO)
2
Sm(THF)
4
, (where ArO
It was also reported that “living”
e
¼
2,6-di-
-butyl-4-methyl-phenoxy) yielded 98% conversion in toluene at 60
C in 1 h. The central ions and
ligands appear to have an effect on the activity of the catalyst [
110
].
tert
5.8.4 Special Catalysts for Polymerizations of Lactones
Some lactones can polymerize in the presence of compounds like alcohols, amines, and carboxylic
acids without additional catalysts. The reactions, however, are slow and yield only low molecular
weight polymers [
95
]. Exception is polymerizations of pivalolactone in the presence of cyclic amines
that yield high molecular weight polyesters at high conversion [
111
]. The initiating steps result from
formations of adducts, amine-pivalate betaines:
N
O
slow
+
N
O
COO
N
O
fast
+
COO
O
slow
N
O
COO
O
O
N
O
n
The above reaction appears to be restricted to highly strained lactones and may not work with larger
lactones [
95
], For instance, when polymerization of
-valerolactone is initiated with ethanolamine at
temperatures up to 200
C there is initially a rapid reaction between the amine group and the monomer:
d
O
O
+
H
2
N
(CH
2
)
4
O
HO
OH
OH
N
4
H
The subsequent reactions, however, are slow:
O
O
O
slow
HO
OH
+
(CH
2
)
4
HO
O
O
N
N
OH
4
4
4
O
H
H
