New photoalignable polyimides and their ability to control liquid-crystal alignment - Polyimides and Other High Temperature Polymers - page 116

Figure 1. Chemical structures of photosensitive polyimides synthesized in this study.

groups into the polymer. Soluble 6F-HAB polyimide was synthesized directly
from the polycondensation of the respective monomers using isoquinoline as a
catalyst. The obtained polymer was characterized by 1 H NMR spectroscopy. In
the 1 H NMR spectrum in Figure 2a, the proton peak of the hydroxyl side groups
appears at 10.0 ppm while the protons of all the aromatic rings on the polymer
backbone appear over the range of 6.9-8.3 ppm. The amino protons, which can
originate from possible residues of partially imidized 6F-HAB poly(amic acid),
are not detected. The polymer was measured to be 53,400 and 1.87 polydis-

persity by the GPC analysis calibrated with polystyrene standards. In conclusion,
a soluble 6F-HAB polyimide was successfully synthesized with a reasonably high
molecular weight.
To the soluble 6F-HAB polyimide, cinnamoyl (CI) and 7-ethoxy-4-
methylcoumarin (ETCOU) side groups were incorporated giving, respectively,
6F-HAB-CI and 6F-HAB-ETCOU. 1 H NMR spectra measured from the polymers
are presented in Figures 2b and 2c. Neither polymer shows the proton peak origi-
nating from the hydroxyl groups of 6F-HAB polyimide. This indicates that the
6F-HAB-CI and 6F-HAB-ETCOU polymers were successfully prepared from the
6F-HAB polyimide. All the polymers obtained always formed good quality thin
films through a conventional solution spin-casting and subsequent drying process.
The glass transition temperature T g and the degradation temperature T d were,
respectively, 181

M w

° C and 340 ° C for 6F-HAB-CI polymer and 132 ° C and 300 ° C for

6F-HAB-ETCOU polymer. For 6F-HAB polymer, the T d was 440 ° C but the T g

could not be detected in the range 50-400 C. Overall, both T g and T d of 6F-HAB

polymer are lowered by incorporating photosensitive side groups.

°