Chemistry Reference
In-Depth Information
In this scheme, chain transfer to monomer must be absent and the termination is well defined.
Termination:
R
MeX
n+1
R
X
+
MeX
n
where X is a halogen, Me is a metal.
This allows formation of macromolecules with terminal halogens. They can be used to initiate new
and different polymerizations.
Three methods were developed to overcome transfer to monomer [
424
]. These are: (1) use of
inifers
; (2) use of proton traps; and (3) establishing conditions under which the rate of termination is
much faster than the rate of transfer to monomer. The first one, the inifer method, is particularly useful
in formation of block copolymers. It allows preparation of
head
end
a
o
and
(
and
) functionalized
telechelic polymers. Bifunctional initiators and transfer agents (
inifers
) are used. The following
illustrates the concept [
424
]:
Ion generation:
XR
þ
MeX
nþ
1
XRX
þ
MeX
n
Ð
Cationization and propagation:
n
XR
XR
+
XR
n-1
Chain transfer with inifers:
XR
XRX
+
n-1
XR
X
+
XR
n-1
XR
EX
R
n-1
n-1
