Chemistry Reference
In-Depth Information
of the use of AB monomers over AA-BB monomers is the lack of sensitivity
employing Novozym 435 and Ru-catalyst
2
was slow (170 h) but did result in
chiral polymers of good molecular weight and
ee
. For example, polymerization of
Me-7HO resulted in a polymer with an
M
p
of 16.3 kDa and an
ee
of 92%.
3.4.3
Chiral Polymers from Racemic
ω
-Methylated Lactones
As described above, 6-MeCL was found to be unreactive in a Novozym-435-
catalyzed polymerization reaction as a result of the formation of an unreactive
(
-alcohols are not accepted as a nucleophile by
Novozym 435 since the lipase-catalyzed transesterification is highly
S
)
-alcohol chain. These
(
S
)
-selective
for the nucleophile. van As et al. proposed that by combining Novozym-435-
catalyzed ring-opening of 6-MeCL with racemization of the terminal alcohol, it
tandem catalysis (ITC) since chain propagation can only be achieved by a combi-
nation of two fundamentally different catalytic systems. The proof-of-principle was
shown by the polymerization of
(
R
)
(
S
)
(
S
)
-6-MeCL, the preferred enantiomer
O
OH
+
O
S
Novozym 435
n = 0
O
R
O
OH
O
S
O
n
O
Novozym 435
n = n + 1
Ru
O
HN
NH
S
Ph
O
O
R
O
OH
O
R
O
n
O
O
Novozym 435
n = n + 1
R
Scheme 12
Chiral polymers from racemic
ω
-methylated lactones by iterative tandem catalysis
