Modern Polymer Spect..

about 1.5 s for 28 "C. The shape of the response curves are similar and can be
described as exponential. The reorientation starts without time delay when the
polarity of the applied field is changed. This means, that there is no retardation
in the response of different structural segments. No distinct differences have been
found in the orientation rates of the flexible and the rigid part of the molecules
of ferroelectric nonpolynieric LCs [53, 581. However, it has been shown that the
molecular motion cannot be described by a single exponential process but consists
primarily of a fast and a subsequent slow process [52]. This motion also includes
confornia tioiial changes in the flexible part of the molecule. In the polymeric ferroelectric
system under investigation, such conforniational changes may take place
in the spacer and the main chain. Due to the lack of conformationally sensitive
absorptions in the FLCP, we were not able to detect or differentiate such changes.
Taking into account the assignment of the absorption bands under consideration
and their dichroic changes during poling the electric field, we can conclude from
Figure 2-28 [83] that not only the mesogen but also the spacer and the main chain
(at least some molecular groups which are in the neighborhood of the spacer attachment
to the backbone) take part in the reorientation process during poling the
electric field. This picture, however, is not supported by the 2D-correlation analysis,
which shows, that there is a strong correlation between the ring-stretching bands
(1506, 1607 cm-') and the two carbonyl bands around 1750 cni-' [16]. This is evidence
that the mesogen reorients as a rigid unit. The strong correlation in the synchronous
spectrum and no appreciable asynchronicity in the asynchronous spectrum
between the mesogen bands and the v(CH2) bands (2926 and 2855 cin-'),
which are mainly due to the spacer, indicates that the mesogen aiid the spacer
reorient synchronously. Figure 2-29 compares the power spectrum of the FLCP to
the reference spectrum (average spectrum of a reorientation process). One can easily
notice, that the intensities of the spacer bands in the power spectrum are considerably
reduced relative to the mesogen bands. Based on these data, we have to coiiclude
that only a small part of the spacer, directly attached to the mesogen, takes
part in the reorientation. The 2D analysis does not supply any evidence that the
main chain of the FLCP participates in the reorientation. Based on these data, the
picture shown in Figure 2-30 can be derived for the response of the FLCP to a
poled electric field.
2.6 Alignment of Side-Chain Liquid-Crystalline
Polyesters Under Laser Irradiation
It has been demonstrated that the photo-induced orientation of dye-containing
SCLCPs can be used for reversible optical data storage [85-901. FTIR polarization
spectroscopy has been applied to monitor the orientation of the main chain and the
mesogenic side-chains which are of critical importance in these storage processes
[15, 91-94]. Here, some results obtained by laser irradiation of a homologous series