Chemistry Reference
In-Depth Information
The ease of forming the smectic mesophase by this class of side-group
type liquid crystalline polymers has rendered a great possibility in syn-
thesizing polymeric chiral smectic materials useful in non-linear optics,
transducers, pyroelectric detectors and display devices (Chapter 6). The
first polymer forming a chiral smectic-C phase was synthesized by Shibaev
et al
. (1984). It has a polymethacrylate main chain, a long polymethylene
spacer, and a mesogenic unit attached at the end with a chiral moiety (poly-
mer
). Since then, a lot of polymers with chiral mesophases have been
synthesized and studied (Le Barny and Dubois, 1989).
3
.
60
CH
3
CH
C
2
CH
3
CH
2
COO
COO
O
CO
COOCH
2
CH
C
2
H
5
10
*
g 20-30 S
C
∗
73-75 S
A
83-85 I.
3.60
It is worthy to note at this point that the polymerization of mesogenic
monomers with chiral moieties does not necessarily result in polymers with
the chiral liquid crystalline phase. For example, Finkelmann (1982) reported
that homopolymers of chiral monomers yielded only smectic mesophases.
On the other hand, copolymerization of chiral monomers with different
spacers or of a chiral monomer and a nematic monomer has been proven
effective and convenient for synthesizing chiral liquid crystalline polymers.
Other attempts at synthesizing chiral smectic polymers have reached
the conclusion that no general conclusion can be made so far as for what
molecular structure will yield the desired phase. Again, all the structural
elements including the main chain, the spacer, and the mesogenic unit are
playing a part. Nevertheless, a longer spacer and more flexible main chain
seem to favor the chiral S
C
phase (Le Barny and Dubois, 1989).
3.6. LIQUID CRYSTALLINE POLYMERS OF
THE SIDE-GROUP TYPE WITH SIDE-ON
ATTACHMENT AND “MESOGEN-JACKETED
LIQUID CRYSTAL POLYMERS”
We have emphasized in Section 3.5, the concept of coupling between
motions of main chain and side groups in side-group type liquid crystal
