Chemistry Reference
In-Depth Information
A variation in controlled/“living” polymerization of vinyl acetate by the use of a bidentate ligand,
2,2
0
-bipyridyl and TEMPO composition in 2:1.2 ratio that was reported by Mardare and
Matyjaszewski [
267
]. The following mechanism was proposed.
(1) Pentacoordinated complexes (I) are formed at a molar ratio of 1.1
R
R
N
N
R
Al
Radicals
Al
+
N
?
N
R
R
R
I
O
R
N
Al
N
N
N
+
R
Al
O
N
N
R
II
N
N
O
O
N
R
N
R
R
Al
+
Al
R
N
N
O
O
N
N
IVa
IIa
i
(2) The irreversible attacks by TEMPO on the pentacoordinated complexes, (Al(
Bu)
3
):BPy (I), lead
to relatively stable and delocalized radicals(II). TEMPO also reacts with some short-lived radicals
present at stage (1) to form alkoxyamines and pentacoordinated complexes of type IV. The
radicals II could be in equilibrium with tiny amounts of very reactive radicals R capable of
initiations and subsequent propagations.
Aldabbagh and coworkers [
269
] reported that carrying out the nitroxide-mediated polymerization
in supercritical carbon dioxide allows improved control of the reaction.
Nesvadba and coworkers [
270
] used nitrones in controlled radical polymerization of vinyl
monomers. This was the beginning of the in situ
NMP
concept. The alkoxyamines were prepared
