Chemistry Reference
In-Depth Information
O
OLi
O
O
OMe
N
Li
Li
OLi
O
O
199
200
201
202
Ph
OLi
OLi
Ph
Li
Ph
Me
2
N
Ph
203
204
205
O
O
Initiator
C
N
R
198
N
R
n
Me
Ph
R =
Bu
Me
Ph
198a
198b
198d
198e
198c
OMe
Cl
Me
Me
198f
198g
198h
198i
Scheme 13.21.
13.3.1.6. Polymerization of Carbodiimides
Helix - sense - selective polymerization of
achiral carbodiimides (
206
) with optically active titanium catalysts has been developed
to yield single-handed helical polycarbodiimides (
207
) (Scheme 13.22 ) [287,288] . The
stability of the helix depends on the bulkiness of
N
- substituents of carbodiimides. For
example, the polymer
207a
-
207c
underwent racemization of the backbone at elevated
temperature, whereas the polymer
207d
, which has two
ortho
- substituents, never race-
mized under the same conditions.
13.3.1.7. Polymerization of Thiophenes
Electrochemical polymerization has been
used to produce a variety of conjugated polymers such as polypyrrole and polythio-
phene, which are usually obtained as an optically inactive form. Asymmetric polymeriza-
tion of thiophenes has been achieved by using chiral nematic liquid crystal (N*-LC)
as an effective chiral scaffold. Thus, optically active poly(3,4-ethylenedioxythiophene)
(
209
) was successfully synthesized by electrochemical polymerization of 3,4-
