Chemistry Reference
In-Depth Information
Propagation
O
O
slow
SnCl
4
O
O
CH
2
fast
O
O
CH
2
O
O
SnCl
4
SnCl
4
2
2
O
CH
2
O
O
O
O
2
O
CH
2
O
O
SbCl
4
O
O
O
CH
2
CH
2
CH
2
O
O
O
O
SnCl
4
SnCl
4
O
O
O
CH
2
O
O
+
O
Termination
CH
2
O
O
CH
2
O
O
SnCl
4
SnCl
3
O
O
O
O
CH
2
Cl
O
n
O
CH
2
n
The initiation step depends upon formation of oxonium ions. Because a carbon cation intermediate
is indicated, it was suggested [
4
] that the propagation probably occurs by ether exchange that results
from a nucleophilic attack by the monomer on the oxonium ion.
Boron trifluoride forms complexes with oxygen-containing compounds, like water, alcohols, and
ethers. When it initiates the polymerization of epoxides, it can associate simultaneously with several
different moieties. These are the monomeric cyclic ethers, as well as the open-chain polymeric ether
groups, and the hydroxy groups on the chain ends. In addition it can also associate with the hydroxy
groups of water. The following illustration shows the type of equilibrium that can take place [
2
]:
BF
3
BF
3
H
R'
R
O
O
R
H
OR
O
R'
+
R
H
OR
+
ROH
