of aromatic polyimides showing various properties have been systematically synthesized using various chemical structures. The difference in polyimide molecular
ordering seems to be closely related to their heat resistance property (i.e.,
T g = 427
C). Phenyl group π–π
à transitions between polymer segments are
expected to occur easily. Therefore, in Fig. 7, the observed Nos. 1 and 2 peak
positions shifted to lower energy compared with the calculated position. The CT
interaction between polymer segments strongly depended on the photoreaction upon
LPUV irradiation.
This result indicates that the chemical structure changes with the excitation of the
C=O double bonds and C-H bonds and the formation of hydroxyl group O-H between
the intermolecular polymer segments through the LPUV irradiation mechanism of
6FDA-TeMPD, as schematically shown in Fig. 9. The CTC structure of 6FDATeMPD was MLP, which is similar to the sandwich structure presented in a previous
study (Kanehashi et al. 2011). The electron-donating benzene ring and the electronaccepting imide ring formed CTCs between both sides of the polymer chains in this
MLP structure (Fig. 9a). Therefore, the photoreaction between the C=O group of the
imide ring and a CH 3 group upon LPUV irradiation occurred in one direction (Fig. 9b);
hydroxyl group O-H was newly formed on the side chain. In the case of polymers with
a symmetric structure, such as 6FDA-TeMPD, the combinations with alternating
sequences to both cross sides clearly formed (Fig. 9c). This result is in a good
agreement with that of the IR and UV spectra shown in Figs. 4 and 5, respectively.
The polarization microscope (POM) images of all 6FDA-based polyimides in the
current study are presented in Fig. 10. The photoalignment characteristic of all LPUV
unirradiated 6FDA-based polyimides was not observed. The photoalignment characteristic of LPUV irradiation at 10 J/cm
2 was also not observed in 6FDA-mPD, 6FDAMPD, and 6FDA-TMPD, as well as in the LPUV unirradiated 6FDA-based polyimide.
However, in the case of 6FDA-TeMPD, the photoalignment characteristic of LPUVirradiated polyimides was observed. The photoalignment characteristic of LPUVirradiated 6FDA-TeMPD was estimated to depend strongly on the photoreaction
between the C=O group of the imide ring and a CH 3 group for the phenyl group
π–π
à transitions based on Fig. 9. The CTCs easily formed in polymers with a large
substituent, alternating sequence, and polarizability, such as 6FDA-TeMPD. Because
of the photoreaction in the CTC structure, only 6FDA-TeMPD showed photoalignment of the LC molecule. However, 6FDA-mPD, 6FDA-MPD, and 6FDATMPD, which form CTC structures with difficulty, did not show photoalignment of
the LC molecules. The chemical and physical structures of the polymer and polymer
cohesiveness strongly affected the photoalignment of the LC molecules.
Photoreactivity of 6FDA-TeMPD Polyimide Prepared with Various
Film Preparation Protocols as an LC Photoalignment Film
Several studies have investigated the effects of different preparation conditions
on the physical chemistry of condensation polymerization. However, the effects
of the preparation protocol on the photoreactivities and LC alignments of
504
S. Sato et al.
ordering seems to be closely related to their heat resistance property (i.e.,
T g = 427
C). Phenyl group π–π
à transitions between polymer segments are
expected to occur easily. Therefore, in Fig. 7, the observed Nos. 1 and 2 peak
positions shifted to lower energy compared with the calculated position. The CT
interaction between polymer segments strongly depended on the photoreaction upon
LPUV irradiation.
This result indicates that the chemical structure changes with the excitation of the
C=O double bonds and C-H bonds and the formation of hydroxyl group O-H between
the intermolecular polymer segments through the LPUV irradiation mechanism of
6FDA-TeMPD, as schematically shown in Fig. 9. The CTC structure of 6FDATeMPD was MLP, which is similar to the sandwich structure presented in a previous
study (Kanehashi et al. 2011). The electron-donating benzene ring and the electronaccepting imide ring formed CTCs between both sides of the polymer chains in this
MLP structure (Fig. 9a). Therefore, the photoreaction between the C=O group of the
imide ring and a CH 3 group upon LPUV irradiation occurred in one direction (Fig. 9b);
hydroxyl group O-H was newly formed on the side chain. In the case of polymers with
a symmetric structure, such as 6FDA-TeMPD, the combinations with alternating
sequences to both cross sides clearly formed (Fig. 9c). This result is in a good
agreement with that of the IR and UV spectra shown in Figs. 4 and 5, respectively.
The polarization microscope (POM) images of all 6FDA-based polyimides in the
current study are presented in Fig. 10. The photoalignment characteristic of all LPUV
unirradiated 6FDA-based polyimides was not observed. The photoalignment characteristic of LPUV irradiation at 10 J/cm
2 was also not observed in 6FDA-mPD, 6FDAMPD, and 6FDA-TMPD, as well as in the LPUV unirradiated 6FDA-based polyimide.
However, in the case of 6FDA-TeMPD, the photoalignment characteristic of LPUVirradiated polyimides was observed. The photoalignment characteristic of LPUVirradiated 6FDA-TeMPD was estimated to depend strongly on the photoreaction
between the C=O group of the imide ring and a CH 3 group for the phenyl group
π–π
à transitions based on Fig. 9. The CTCs easily formed in polymers with a large
substituent, alternating sequence, and polarizability, such as 6FDA-TeMPD. Because
of the photoreaction in the CTC structure, only 6FDA-TeMPD showed photoalignment of the LC molecule. However, 6FDA-mPD, 6FDA-MPD, and 6FDATMPD, which form CTC structures with difficulty, did not show photoalignment of
the LC molecules. The chemical and physical structures of the polymer and polymer
cohesiveness strongly affected the photoalignment of the LC molecules.
Photoreactivity of 6FDA-TeMPD Polyimide Prepared with Various
Film Preparation Protocols as an LC Photoalignment Film
Several studies have investigated the effects of different preparation conditions
on the physical chemistry of condensation polymerization. However, the effects
of the preparation protocol on the photoreactivities and LC alignments of
504
S. Sato et al.