Chemistry Reference
In-Depth Information
Termination
O
O
O
O
O
+
O
n
O
O
O
O
O
n+1
O
Acetate groups are present at both end of the polymer molecules as shown above [
78
]. This was
confirmed by analytical evidence. The initiation of dioxolane polymerization is pictured differently [
79
,
80
]:
(C
2
H
5
)O
BF
3
+
(C
2
H
5
)O
+
O
O
BF
3
O
O
+
O
BF
3
BF
3
O
O
O
O
O
O
O
OO
+
O
O
O
O
O
O
Chain cleavage can occur as a result of BF
3
complexation with an oxygen in a chain [
80
]:
O
OO
O
BF
3
BF
3
There is some disagreement about the nature of the end groups. and there are some speculations
that the polymers might possess large cyclic structures. Nevertheless, polymerizations initiated with
benzoyllium hexafluoroantimonate (C
6
H
5
CO
+
SbF
6
) and conducted at
15
C in nitromethane or
methylene chloride result in mostly linear polymers. The terminal end groups come from terminating
agents that are deliberately added [
81
]. These polymerizations proceed without any appreciable
amounts of transfer reactions, affecting the DP.
5.7.3 Polymerization of Dioxopane and Other Cyclic Acetals
Polymerization of six membered cyclic formals has, apparently not been explored [
1
]. Polymerization
of 1,3-dioxopane can be initiated by camphor sulfonic acid [
82
,
83
]:
O
O
OO
n
