Modern Polymer Spect..

Figure 2-33. Instrumental details of the apparatus used for on-line FTIR measurements during
laser irradiation.
perpendicular to the argon-ion laser beam polarization direction, respectively. The
irradiated sample area was about 3 mm’.
2.6.3 Results and Discussion
In the FTIR polarization spectra of the films prepared by casting from solution
no dichroism could be detected before laser irradiation. Figure 2-34 shows the
polarization spectra of a P8a12 polyester after irradiation with the 488 nm argonion
laser line (laser power 800 mW/cm’, irradiation time 1000 s). A detailed assignment
of the individual absorptions bands to specific structural units is given in
Table 2-3. The observable dichroic effects clearly demonstrate the significant orientation
induced in the different functionalities of the polymer. Thus, the mesogenic
side groups are preferentially oriented perpendicular to the polarization direction
of the laser beam. This picture is based on the 0-dichroism of the v(C-N) band and
the aromatic ring modes (see also Table 2-3). Additionally, the 7c-dichroism of the
v(CH2) absorptions indicates a perpendicular orientation of the side and main
chains relative to the laser beam polarization direction, whereas the smaller K-
dichroism of the ester linkage indicates a somewhat lower orientation. As the electromagnetic
radiation influences only the orientation of the mesogenic groups with