Modern Polymer Spect..

56 2 Segrnental Mohilitj~ of Liquid Crystals arid Lirjuid-C~.vstallirie Polymers
(mole ratio 0.95 : 0.05 : 2.70)
C=O N
I II
? v
o y 0 I 0
8 "C 55 'C 73 'C
G-S:e---,S,c---*I
Figure 2-23. Chemical structure,
coniposition and transition
temperatures of the side-chain
FLCP under investigation.
[77, 781. Since the spacer is effectively decoupling the movement of the mesogen
froni the polymer backbone, a different behavior of mesogen, spacer, and main
chain can be expected in a reorientation process. So far, most of the research on the
mobility of FLCPs has been limited to the determination of relaxation times by
using dielectric spectroscopy [79] or response times by using electro-optical switching
studies [80] without differentiation of the motions of individual functionalities
in the macromolecule and only few time-resolved vibrational spectroscopic measurements
are available on this subject [81-831. However, the movements of the
individual segments control the reorientation process and hence, the study of their
dynamics is a key to understand the behavior of an FLCP in an electric field. Based
on the recent advances in data-acquisition techniques [ 161 we have attempted in
the present work to follow the reorientation dynamics of the different segments of
an FLCP from one stable state to another on the submillisecond time scale during
poling of an electric field [83].
2.5.5.1 Materials
The chemical structure, composition and the transition temperatures of the investigated
side-chain FLCP are shown in Figure 2-23. The molecular weight of this
polymer is approximately 18800 and the synthesis and characterization have been
described in detail elsewhere [84].
2.5.5.2 Experimental
The variable-temperature cell was the same as described in Section 2.5.2, the only
difference being that a spacer with a uniform thickness of 5 pm was used between
the electrodes. The empty cell and the FLCP were heated to 90 "C to introduce the