Proton conducting polyimides from novel sulfonated diamines - Polyimides and Other High Temperature Polymers - page 148

Figure 3. Schematic diagrams showing different intrasegmental mobilities for ODADS and BDSA-
based polyimides.
NTDA-BDSA/BAPF(1/1) and NTDA-BDSA/BAPHF (1/1) despite a less rigid
structure of the former; i.e., the favorable effect of the less rigid structure of
NTDA-BDSA/ODA(1/1) on water stability was offset by the unfavorable effect
of the higher water uptake. In contrast, for the “flexible”-type copolyimides, the
reduction of the IEC (and therefore the water uptake) by changing the non-
sulfonated diamine moiety led to great improvement in water stability of the
membranes. NTDA-ODADS/BAPB(1/1) displayed the best water stability among
ODADS-based polyimide membranes because of its highly flexible structure and
the lowest IEC.
On the other hand, although BAPFDS is a typical rigid and bulky diamine
monomer, the stability of BAPFDS-based copolyimide membranes is not so poor
as expected. In fact, BAPFDS-based copolyimide membranes displayed much
better water stability than BDSA-based ones with the same non-sulfonated dia-
mine moiety (ODA) and similar IEC. As shown in Table 3, NTDA-BAPFDS
/ODA(2/1) had much better water stability than NTDA-BDSA/ODA(1/1) despite
slightly larger IEC of the former. NTDA-BAPFDS/ODA(1/1) and NTDA-
ODADS/BAPF(1/1) had the same IEC and chain flexibility, and the difference in
structures between the two kinds of copolyimides is only that the sulfonic acid
groups are attached to different diamine moieties. However, NTDA-BAPFDS