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Scheme V. Preparation of polyimides derived from various commercial dianhydrides.
2.5. Characterization
The
13
C and
1
H NMR spectra were obtained using a JEOL EX-400 instrument op-
erating at 100.40 MHz for carbon and 399.65 MHz for proton. The inherent vis-
cosities of all pol
y(et
her imide)s were measured using Ubbeloh
de
viscometer.
Weight-average (
) were de-
termined by gel permeation chromatography (GPC). Four Waters (Ultrastyragel)
columns were used for GPC analysis with tetrahydrofuran (THF) (1 mL
.
min
-1
) as
Mw
) and number-average molecular weights (
Mn
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