Proton conducting polyimides from novel sulfonated diamines - Polyimides and Other High Temperature Polymers - page 138

2.3. Polymerization
Sulfonated polyimides were prepared by a one-step method in m-cresol. The syn-
thesis procedures for the homopolyimides are described as follows using NTDA-
ODADS as an example.
0.540 g (1.5 mmol) of ODADS, 5.0 mL of m-cresol, and 0.36 g (3.6 mmol) of
triethylamine were successively added to a 100 ml completely dried 4-neck flask
under nitrogen flow with stirring. After ODADS was completely dissolved, 0.402
g of NTDA (1.5 mmol) and 0.26 g (2.13 mmol) of benzoic acid were added. The
mixture was stirred at room temperature for a few minutes, and then heated at
80°C for 4 h and 180°C for 20 h. After cooling to about 100°C, additional 10-20
mL of m-cresol was added to dilute the highly viscous solution, which was then
poured into 100 mL of acetone. The fiber-like precipitate was filtered off, washed
with acetone, and dried in vacuum.
The various random copolyimides were prepared in a similar way to that for
the homopolyimides. A typical procedure is described as follows using NTDA-
ODADS/ODA(1/1) as an example.
0.360 g (1.0 mmol) of ODADS, 6.0 mL of m-cresol, and 0.24 g (2.4 mmol) of
triethylamine were successively added to a 100 ml completely dried 4-neck flask
under nitrogen flow with stirring. After ODADS was completely dissolved, 0.200
g (1.0 mmol) of ODA, 0.536 g (2.0 mmol) of NTDA, and 0.34 g (2.8 mmol) of
benzoic acid were added. The mixture was stirred at room temperature for a few
minutes and then heated at 80°C for 4 h and 180°C for 20 h. After cooling to
around 100°C, additional 10-20 mL of m-cresol was added to dilute the highly
viscous solution, which was then poured into 100 mL of acetone. The fiber-like
precipitate was filtered off, washed with acetone, and dried in vacuum.
2.4. Film formation and proton-exchange
Polyimide films (in triethylammonium salt form) were prepared by the conven-
tional solution cast method. NTDA-BAPBDS, NTDA-ODADS/BAPB(1/1),
NTDA-BDSA/ODA(1/1), and NTDA-ODADS/ODA(1/1) copolyimide films
were prepared by casting their m-cresol solutions onto glass plates or dishes and
dried at 120°C for 10 h. Other polyimide films were prepared by casting their
DMSO solutions at 80°C for 10 h. The as-cast films were soaked in methanol at
60°C for 1 h to remove the residual solvent, and then the proton exchange was
performed by immersing the films into 1.0 N hydrochloric acid at room tempera-
ture for 5-10 h. The films in proton form were thoroughly washed with de-ionized
water and then dried in vacuum at 150°C for 20 h. The thickness of the films was
in the range of 20-40 µm.
2.5. Measurements
Infrared (IR) spectra were recorded on a Horiba FT-200 spectrometer using KBr
pellets. 1 H NMR spectra were recorded on a JEOL EX270 (270 MHz) instrument.