polymer is heated above its glass transition temperature and no isotropization is
observed up to 250
C. The phase retains on cooling to the room temperature,
forming a columnar LC glass. It has been proposed that direct attachment of the
long mesogen rigidifies the backbone into an extended cylindrical conformation. As
the mesogen is so much longer than the repeat unit of the backbone, the angle
between the long axis of the mesogen is about 51–57
with respect to the column/
chain axis.
A polysiloxane with the same mesogenic side-group, at a DP of 35 (P2 in Chart 5),
also exhibits a Col h phase (Zhang et al. 2010). The ordered phase develops on heating
and remains upon cooling. If one applies the Flory’s rigid-rod argument (Flory 1956)
to this polymer and assumes that the MW is the lower limit MW to show the columnar
LC phase, the distance along the column axis direction between two adjacent
Fig. 6 X-ray diffraction
patterns of C6 in its Col h
phase at 25
C (bottom) and
100
C (top). (Adapted from
Tokita et al. 2013 Copyright
(2013), with permission from
Elsevier)
P3
P1
P2
PmVT
PVTMS
M3
Chart 5 Structures of a few columnar LC phase-forming polymers with a rigidified chain
5 Columnar Phase-Forming Polymers
129