Enhanced hydrolytic stability of sulfonated polyimide ionomers using bis(naphthalic anhydrides) with low electron affinity

Abstract

In the pursuit of hydrolytically stable sulfonated polyimide (SPI) membranes as promising candidates for proton exchange membranes, usable at elevated temperature, a series of novel SPI ionomers based on the low electron affinity bis(naphthalic anhydrides), 4,4 0 -sulfide-bis(naphthalic anhydride) (SBNA) and benzophenone-4,4 0 -bis(4-thio-1,8-naphthalic anhydride) (BPBTNA), were prepared. Tough, flexible, and transparent membranes were obtained from these polymers, although their inherent viscosities ranged from 0.41 to 0.59 dL g À1 . The SPI membranes were thermally stable with the decomposition of sulfonic acid groups over 300 C, and exhibited good mechanical properties with 65 MPa of tensile strength at 25 C and 50% RH. The proton conductivities of the SPI membranes increases with increasing temperature and ion exchange capability (IEC), and the S-O(80) with 2.23 mequiv. g À1 of IEC showed a higher proton conductivity than Nafionâ 212 at 100% RH. For the high IEC membranes, microscopic analyses revealed the hydrophilic clusters were well-dispersed and connected to each other. The accelerated water stability tests demonstrated that the SPI ionomers based on SBNA and BPBTNA maintained a high mechanical strength after being aged in water for 24 h at 140 C, which was much more stable than the SPI membranes based on 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA). The improved hydrolytic stability of polymers could be well correlated with the results of the electron affinity (E a ) of the dianhydride calculated by the theoretical calculation. This investigation illustrated that this strategy will benefit the further development of hydrolytically stable SPIs applied to high temperature PEFCs.

Synthesis and characterization of sulfonated block copolyimides derived from 4,4'‐sulfide‐bis(naphthalic anhydride) for proton exchange membranes

“…4,4′‐Diamonodiphenyl ether‐2,2'‐disulfonic acid (ODADS) and 4,4′‐sulfide‐bis(naphthalic anhydride) (SBNA) were prepared according to the reported procedures.…”

“…However, because of the hydrolytic instability of imide moiety in the SPIs, which affects the lifetime of membranes in fuel cell application, a lot of novel SPIs have been designed and synthesized using naphthalene tetracarboxylic dianhydride (NTDA) with many high basic sulfonated diamines to enhance their hydrolytic stability . In addition, the hydrolytic stability of SPIs also could be improved by using dianhydrides with low electron affinity, such as 4,4′‐binaphthyl‐1,1',8,8'‐tetracarboxylic dianhydride (BNTDA), benzophenone‐4,4′‐bis(4‐thio‐1,8‐naphthalic anhydride) (BPBTNA) . Recently, our group has reported the SPIs obtained from another dianhydride monomer with calculated electron affinity ( E a) value of 2.03 eV, 4,4′‐sulfide‐bis(naphthalic anhydride) (SBNA), showed comparable hydrolytic stability and higher proton conductivity .…”

“…In addition, the hydrolytic stability of SPIs also could be improved by using dianhydrides with low electron affinity, such as 4,4′‐binaphthyl‐1,1',8,8'‐tetracarboxylic dianhydride (BNTDA), benzophenone‐4,4′‐bis(4‐thio‐1,8‐naphthalic anhydride) (BPBTNA) . Recently, our group has reported the SPIs obtained from another dianhydride monomer with calculated electron affinity ( E a) value of 2.03 eV, 4,4′‐sulfide‐bis(naphthalic anhydride) (SBNA), showed comparable hydrolytic stability and higher proton conductivity . However, only random SPI membranes were investigated to relate their structure and property relationships in these reports.…”

Proton-Exchange Membranes Based on Sulfonated Polymers

“…8) 52,61,68 69 ; introducing the bulky unit into the main or side chain of polyimide 70,71 and the electron-donating bridging sulfur atoms [72][73][74] phenoxy groups 75 , benzophenone groups 76 into the main chain; the use of bi-naphthalene system (Fig. 11) 77,78 ; introducing sulfonic groups into the side chain rather than the main chain of the polyimide to reduce their electron-accepting effects 71,79 .…”

Synthesis and characterization of acid–base polyimides bearing pendant sulfoalkoxy groups for direct methanol fuel cell applications

“…These sulfonated polymers include sulfonated poly(arylene ether)s (SPAEs), [7][8][9] sulfonated polyimides (SPIs), [10][11][12] sulfonated polybenzimidazole (SPBI), 13,14 and sulfonated polyphenylenes (SPP). 15,16 Among these polymers, SPIs are considered as a competitive candidate for PEM applications owing to their high mechanical strength, high thermal stability, good film-forming ability, and low fuel permeation.…”