Chemistry Reference
In-Depth Information
and chiral cobalt catalyst (
9
) [205, 206]. Although the obtained polymers were mostly
insoluble in common solvents due to the high degree of polymerization, the THF-soluble
fraction exhibited optical activity. The highest value of optical rotation was obtained in
the polymerization of
124
, using
9
as a catalyst to give a polymer showing [
α
]
365
+1379 ° ,
which is corresponding to 78% excess of helical sense.
O
O
O
O
O
O
O
2
2
(
−
)-
140
(
−
)-
141
SH
SH
SH
OH
OH
OH
(+)-
142
(
−
)-
142
(
−
)-
143
(-)-
144
(+)-
145
(+)-
146
13.3.1.1.3. Other Acrylic Monomers
The control of stereochemistry in the polymeriza-
tion of acrylates and acrylamides is more diffi cult than that in the polymerization of
methacrylates. Catalytic helix-sense-selective polymerization of acrylates (
147
,
148
) has
been investigated by using various chiral ligands [208,209]. Among the diamine ligands
examined, (+) -
PMP
and (+) -
DDB
showed high activity in the polymerization of
147
and
148
to give the optical rotations of [
94 ° (poly -
148
with (+) -
DDB
), respectively. The isotacticity was estimated to be 61-70%, which
was high enough to form a single-handed helical conformation.
The anionic polymerization of bulky acrylamides (
149
-
158
) has been initiated by
organolithium/(
α
]
365
+102 ° (poly -
147
with (+) -
PMP
) and
−
) -
Sp
, which was shown to be a better catalytic system than
DDB
and
PMP
complexes [210-215]. Although polyacrylamides were obtained generally in high
yield with a narrow molecular weight distribution, the isotacticity was comparatively low
to give a mixture of
meso -
and
racemo
- diads. The highest isotacticity (m = 87%) and
optical activity ([
−
α
]
365
−
657°) were achieved in the polymerization of
158h
using the
FlLi/
(
98 ° C [213] . Asymmetric coordination polymeriza-
tion of acrylamides by optically active zirconocene catalyst (
164
) has been recently
developed [216,217]. Optically active, single-handed helical poly-
149
and poly -
158h
and
their copolymers with methacrylate blocks were obtained in almost quantitative yield
by using
164
as a catalyst. Radical polymerization of methacrylamides
159
[218] ,
160
[219] , and
161
[220] was carried out in (
−
) -
Sp
complex as an initiator at
−
)-menthol as a solvent to afford optically active,
highly isotactic helical polymers in good yield.
A bulky
−
- (trityloxymethyl)acrylonitrile (
162a
) polymerized in the presence of
FlLi/
(+) -
DDB
to produce insoluble polymers showing an optical rotation of [
α
]
D
+115 °
in suspension, which was completely lost when the trityl groups were removed [221].
Helix-sense-selective polymerization of some other bulky monomers has been attempted
using chiral initiators: Monomers
162b
-
d
[222] and
163a
[179b] did not give polymers
probably due to the highly crowded monomer structures. On the other hand, bulky
α
