Chemistry Reference
In-Depth Information
TABLE 13.1. Asymmetric Polymerization of Methacrylate 127 with DPEDA - L i /(+) - PMP or
FIL i /(+) - PMP in toluene at
−
78 ° C
RLi
127/Li
[ α ]
365
D P
M
w
/
M
n
DPEDA - Li
15
+1325
27
1.04
DPEDA - Li
20
+1406
30
1.08
DPEDA - Li
30
+1651
45
1.13
DPEDA - Li
50
+1675
81
1.12
FILi
15
+1530
30
1.14
FILi
30
+1641
60
1.10
of poly -
131
with
m
-CPBA was also reported although the enantiomeric excess obtained
was up to 19% [199].
Helix-sense-selective polymerization of methyl, benzyl, and
t -
butyl methacrylates was
investigated by using optically active crown ethers (
137
,
138
) and chiral diamine (
139
)
as a ligand to obtain the optically active, helical polymers. However, the polymers gradu-
ally racemized at ambient temperature to give optical rotations close to zero, which
suggests that these esters would be too small to maintain the single-handed helical con-
formation [200,201]. The complexes consisting of BuLi/
109a
and BuLi/
110
were also
examined to fail in producing an optically active, helical polymer in the polymerization
of methyl and benzyl methacrylates [176b].
O
O
O
O
O
O
O
O
O
O
O
O
137
138
N
N
139
Optically active, highly isotactic poly(methacrylate)s having a single-handed helical
conformation are obtained not only by anionic polymerization but also by radical polym-
erization. Although the stereochemical control of radical polymerization is generally
more diffi cult than that of anionic polymerization, some effective methods have
been developed, in which an appropriate choice of monomers and reagents is the key
to success. Thus, the helix-sense-selective polymerization of bulky monomers
such as 1-phenyldibenzosuberyl methacrylate (
124
) [202 - 206] and 9 - phenyl - 9,10 -
dihydroanthracen - 9 - yl methacrylates (
125
,
126
) [207] was achieved by using optically
active initiators (
140
,
141
), chain transfer reagents (
142
,
143
), solvents (
144
-
146
) [204] ,
