The glass transition temperatures of the isotropic, dense, and nonporous 6FDAmPD, 6FDA-MPD, 6FDA-TMPD, and 6FDA-TeMPD polyimide films were
298, 335, 380, and 427
C, respectively (Miyata et al. 2008; Sato et al. 2010, 2011b).
The glass transition temperature was much higher than the temperature used in all of the
optical measurements. Under optical measurement conditions, all of the 6FDA-based
polyimides were glassy and completely amorphous. As the number of methyl groups in
the diamine moiety increased, the glass transition temperature also increased. The
addition of four methyl groups led to an increase of 129
C. Thus, the methyl groups
seemingly restricted the mobility of the polymer segments.
The IR spectra of the LPUV-irradiated 6FDA-based polyimides for 2 J/cm
2 and
unirradiated 6FDA-based polyimides are shown in Fig. 4. 6FDA-mPD: 1786 cm
À1
and 1726 cm
À1 (C=O stretching), 1360 cm
À1 (C–N stretching), and 1346 cm
À1
(C–H bending). 6FDA-MPD: 1786 cm
À1 and 1729 cm
À1 (C=O stretching),
1360 cm
À1 (C–N stretching), and 1345 cm
À1 (C–H bending). 6FDA-TMPD:
1786 cm
À1 and 1728 cm
À1 (C=O stretching), 1358 cm
À1 (C–N stretching), and
1345 cm
À1 (C–H bending). 6FDA-TeMPD: 1786 cm
À1 and 1726 cm
À1 (C=O
stretching), 1354 cm
À1 (C–N stretching), and 1342 cm
À1 (C–H bending). In
Fig. 4a, the IR spectra of 6FDA-mPD, 6FDA-MPD, and 6FDA-TMPD did not
change through LPUV irradiation. However, for 6FDA-TeMPD, the O-H bond
peak intensity near 3500 cm
À1 slightly increased, the C=O bond peak intensity
near 1730 cm
À1 decreased, and the peak intensity near 1360 cm
À1 decreased upon
LPUV irradiation. The C-N and C–H bending peaks were observed in the range
1300–1400 cm
À1 . The IR spectra in this range are shown in Fig. 4b. The peak whose
intensity decreased upon LPUV irradiation is due to the C–H bending of the methyl
group in the diamine moiety.
The result indicates that only the 6FDA-TeMPD chemical structure changes with
excitation of the C=O double bond and C-H bond. In addition, the hydroxyl group
O-H bond was newly formed. However, no photoscission reaction of LPUV irradiation was observed, because the other peak intensities did not change. Therefore, in
the current study, the LPUV reaction was systematically studied through its UV
absorption and MO calculation.
The UV spectra from 3.5 to 6.5 eV of these LPUV-irradiated and unirradiated
6FDA-based polyimides are shown in Fig. 5. Two significant peaks were observed
in the ranges 5.5–5.7 eV (No. 1) and 6.2–6.4 eV (No. 2) in 6FDA-based polyimides. The No. 1 peak position shifted to lower energy as the number of methyl
groups in the diamine moiety increased. The No. 1 peak positions were 5.68 eV for
6FDA-mPD, 5.62 eV for 6FDA-MPD, 5.53 eV for 6FDA-TMPD, and 5.52 eV for
6FDA-TeMPD. In contrast, the No. 2 peak positions did not change. The
No. 2 peak positions were about 6.5 eV for 6FDA-mPD and 6FDA-MPD,
6.21 eV for 6FDA-TMPD, and 6.21 eV for 6FDA-TeMPD. The peak position
remained constant and did not depend on the number of methyl groups in the
diamine moiety.
The photon energy associated with a wavelength of 254 nm is 4.9 eV. This photon
energy was absorbed in all 6FDA-based polyimides used in the current study. A
change in peak intensity was not observed in this photon energy range. However, the
498
S. Sato et al.
298, 335, 380, and 427
C, respectively (Miyata et al. 2008; Sato et al. 2010, 2011b).
The glass transition temperature was much higher than the temperature used in all of the
optical measurements. Under optical measurement conditions, all of the 6FDA-based
polyimides were glassy and completely amorphous. As the number of methyl groups in
the diamine moiety increased, the glass transition temperature also increased. The
addition of four methyl groups led to an increase of 129
C. Thus, the methyl groups
seemingly restricted the mobility of the polymer segments.
The IR spectra of the LPUV-irradiated 6FDA-based polyimides for 2 J/cm
2 and
unirradiated 6FDA-based polyimides are shown in Fig. 4. 6FDA-mPD: 1786 cm
À1
and 1726 cm
À1 (C=O stretching), 1360 cm
À1 (C–N stretching), and 1346 cm
À1
(C–H bending). 6FDA-MPD: 1786 cm
À1 and 1729 cm
À1 (C=O stretching),
1360 cm
À1 (C–N stretching), and 1345 cm
À1 (C–H bending). 6FDA-TMPD:
1786 cm
À1 and 1728 cm
À1 (C=O stretching), 1358 cm
À1 (C–N stretching), and
1345 cm
À1 (C–H bending). 6FDA-TeMPD: 1786 cm
À1 and 1726 cm
À1 (C=O
stretching), 1354 cm
À1 (C–N stretching), and 1342 cm
À1 (C–H bending). In
Fig. 4a, the IR spectra of 6FDA-mPD, 6FDA-MPD, and 6FDA-TMPD did not
change through LPUV irradiation. However, for 6FDA-TeMPD, the O-H bond
peak intensity near 3500 cm
À1 slightly increased, the C=O bond peak intensity
near 1730 cm
À1 decreased, and the peak intensity near 1360 cm
À1 decreased upon
LPUV irradiation. The C-N and C–H bending peaks were observed in the range
1300–1400 cm
À1 . The IR spectra in this range are shown in Fig. 4b. The peak whose
intensity decreased upon LPUV irradiation is due to the C–H bending of the methyl
group in the diamine moiety.
The result indicates that only the 6FDA-TeMPD chemical structure changes with
excitation of the C=O double bond and C-H bond. In addition, the hydroxyl group
O-H bond was newly formed. However, no photoscission reaction of LPUV irradiation was observed, because the other peak intensities did not change. Therefore, in
the current study, the LPUV reaction was systematically studied through its UV
absorption and MO calculation.
The UV spectra from 3.5 to 6.5 eV of these LPUV-irradiated and unirradiated
6FDA-based polyimides are shown in Fig. 5. Two significant peaks were observed
in the ranges 5.5–5.7 eV (No. 1) and 6.2–6.4 eV (No. 2) in 6FDA-based polyimides. The No. 1 peak position shifted to lower energy as the number of methyl
groups in the diamine moiety increased. The No. 1 peak positions were 5.68 eV for
6FDA-mPD, 5.62 eV for 6FDA-MPD, 5.53 eV for 6FDA-TMPD, and 5.52 eV for
6FDA-TeMPD. In contrast, the No. 2 peak positions did not change. The
No. 2 peak positions were about 6.5 eV for 6FDA-mPD and 6FDA-MPD,
6.21 eV for 6FDA-TMPD, and 6.21 eV for 6FDA-TeMPD. The peak position
remained constant and did not depend on the number of methyl groups in the
diamine moiety.
The photon energy associated with a wavelength of 254 nm is 4.9 eV. This photon
energy was absorbed in all 6FDA-based polyimides used in the current study. A
change in peak intensity was not observed in this photon energy range. However, the
498
S. Sato et al.