Chemistry Reference
In-Depth Information
Figure 2.20. N-I transition temperature
T
c
against the molecular weight. (From
Blumstein
et al
. 1984.)
where
N
is the degree of polymerization and
l
0
and
l
are lengths of the
repeat unit and persistence length.
It is known that the persistence length is normally about 2-10 times
that of the repeat units for polymers, depending on the real structure of
polymers. It is seen that the latent entropy is no longer a universal value,
as in the Maier-Saupe theory. Some experimental results has been reviewed
by Luckhurst (1986).
The worm chain in a possible polar nematic phase was discussed as well
(Wang & Lam, 1992). The dipolar interaction was taken into account in
addition to the quadrupolar interaction. It results in the complexity of the
phase diagram.
2.6.
MAIN CHAIN LIQUID CRYSTALLINE
POLYMERS WITH SPACERS
2.6.1.
Molecularly non-homogeneous liquid
crystalline polymers
Most main chain liquid crystalline polymers are composed of mesogenic
units linked by spacers with varying degrees of flexibility, such as repeated
methylene, oxyethylene, or siloxane groups,
etc
., in order to reduce the
